Travis CI: Bump to Ubuntu Bionic 18.04 LTS

Also bump Linux compilers from (GCC 4.8, GCC 4.9, GCC 5, GCC 7,
GCC 8, Clang 3.9, Clang 4.0, Clang 5.0, Clang 6.0) to (GCC 7,
GCC 8, Clang 7, Clang 8). There's no need to test against every
ancient compiler under the sun. Furthermore, we no longer need
an apt sources list for Bionic.

[ci skip] (Tested already <https://travis-ci.org/charybdis-ircd/charybdis/builds/594225622>)

.travis.yml

@@ -4,6 +4,7 @@
 language: c
 
 # Use the faster container-based infrastructure.
+dist: bionic
 sudo: false
 
 notifications:
@@ -14,81 +15,33 @@ notifications:
 matrix:
   include:
     - os: linux
-      compiler: gcc
+      compiler: gcc-7
       addons:
         apt:
-          sources: ['ubuntu-toolchain-r-test']
-          packages: ['gcc-4.8', 'automake', 'autoconf', 'libtool', 'shtool', 'libsqlite3-dev', 'python-sphinx', 'texinfo']
-      env: COMPILER=gcc-4.8
-
-    - os: linux
-      compiler: gcc
-      addons:
-        apt:
-          sources: ['ubuntu-toolchain-r-test']
-          packages: ['gcc-4.9', 'automake', 'autoconf', 'libtool', 'shtool', 'libsqlite3-dev', 'python-sphinx', 'texinfo']
-      env: COMPILER=gcc-4.9
-
-    - os: linux
-      compiler: gcc
-      addons:
-        apt:
-          sources: ['ubuntu-toolchain-r-test']
-          packages: ['gcc-5', 'automake', 'autoconf', 'libtool', 'shtool', 'libsqlite3-dev', 'python-sphinx', 'texinfo']
-      env: COMPILER=gcc-5
-
-    - os: linux
-      compiler: gcc
-      addons:
-        apt:
-          sources: ['ubuntu-toolchain-r-test']
           packages: ['gcc-7', 'automake', 'autoconf', 'libtool', 'shtool', 'libsqlite3-dev', 'python-sphinx', 'texinfo']
-      env: COMPILER=gcc-7
 
     - os: linux
-      compiler: gcc
+      compiler: gcc-8
       addons:
         apt:
-          sources: ['ubuntu-toolchain-r-test']
           packages: ['gcc-8', 'automake', 'autoconf', 'libtool', 'shtool', 'libsqlite3-dev', 'python-sphinx', 'texinfo']
-      env: COMPILER=gcc-8
 
     - os: linux
-      compiler: clang
+      compiler: clang-7
       addons:
         apt:
-          sources: ['ubuntu-toolchain-r-test']
+          packages: ['clang-7', 'automake', 'autoconf', 'libtool', 'shtool', 'libsqlite3-dev', 'python-sphinx', 'texinfo']
-          packages: ['clang-3.9', 'llvm-3.9-dev', 'automake', 'autoconf', 'libtool', 'shtool', 'libsqlite3-dev', 'python-sphinx', 'texinfo']
-      env: COMPILER=clang-3.9
 
     - os: linux
-      compiler: clang
+      compiler: clang-8
       addons:
         apt:
-          sources: ['ubuntu-toolchain-r-test']
+          packages: ['clang-8', 'automake', 'autoconf', 'libtool', 'shtool', 'libsqlite3-dev', 'python-sphinx', 'texinfo']
-          packages: ['clang-4.0', 'llvm-4.0-dev', 'automake', 'autoconf', 'libtool', 'shtool', 'libsqlite3-dev', 'python-sphinx', 'texinfo']
-      env: COMPILER=clang-4.0
-
-    - os: linux
-      compiler: clang
-      addons:
-        apt:
-          sources: ['ubuntu-toolchain-r-test']
-          packages: ['clang-5.0', 'llvm-5.0-dev', 'automake', 'autoconf', 'libtool', 'shtool', 'libsqlite3-dev', 'python-sphinx', 'texinfo']
-      env: COMPILER=clang-5.0
-
-    - os: linux
-      compiler: clang
-      addons:
-        apt:
-          sources: ['ubuntu-toolchain-r-test']
-          packages: ['clang-6.0', 'llvm-6.0-dev', 'automake', 'autoconf', 'libtool', 'shtool', 'libsqlite3-dev', 'python-sphinx', 'texinfo']
-      env: COMPILER=clang-6.0
 
     - os: osx
       osx_image: xcode7.3
       compiler: clang
-      env: COMPILER=clang LIBTOOLIZE=glibtoolize
+      env: LIBTOOLIZE=glibtoolize
 
 cache:
   apt:
@@ -96,8 +49,8 @@ cache:
 
 script:
   - bash autogen.sh
-  - "if [ ${TRAVIS_OS_NAME} != 'osx' ]; then CC=$COMPILER CFLAGS=\"-Werror -Wno-unused-value -Wno-unused-parameter\" ./configure --with-shared-sqlite --with-assert=hard --enable-warnings; fi"
+  - "if [ ${TRAVIS_OS_NAME} != 'osx' ]; then CFLAGS=\"-Werror -Wno-unused-value -Wno-unused-parameter\" ./configure --with-shared-sqlite --with-assert=hard --enable-warnings; fi"
-  - "if [ ${TRAVIS_OS_NAME} = 'osx' ]; then CC=$COMPILER ./configure --with-shared-sqlite; fi"
+  - "if [ ${TRAVIS_OS_NAME} = 'osx' ]; then ./configure --with-shared-sqlite; fi"
   - make -j4
   - "if [ ${TRAVIS_OS_NAME} != 'osx' ]; then make check; fi"
   - make install