Travis CI should run MySQL 5.5 tests on Trusty

.travis.yml

@@ -45,17 +45,11 @@ matrix:
         mariadb: 10.2
         hosts:
           - mysql2gem.example.com
-    - rvm: 2.0.0
+    - rvm: 2.4
       env: DB=mysql55
-      dist: precise
       addons:
         hosts:
           - mysql2gem.example.com
-        apt:
-          packages:
-          - mysql-server-5.5
-          - mysql-client-core-5.5
-          - mysql-client-5.5
     - rvm: 2.4
       env: DB=mysql57
       addons:
@@ -67,7 +61,7 @@ matrix:
         hosts:
           - mysql2gem.example.com
     - os: osx
-      rvm: 2.3
+      rvm: 2.4
       env: DB=mysql56
       addons:
         hosts:
@@ -76,5 +70,5 @@ matrix:
   allow_failures:
     - rvm: ruby-head
     - os: osx
-      rvm: 2.3
+      rvm: 2.4
       env: DB=mysql56

.travis_mysql55.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+set -eux
+
+apt-get purge -qq '^mysql*' '^libmysql*'
+rm -fr /etc/mysql
+rm -fr /var/lib/mysql
+apt-get install -qq mysql-server-5.5 mysql-client-core-5.5 mysql-client-5.5 libmysqlclient-dev

.travis_setup.sh

@@ -2,6 +2,11 @@
 
 set -eux
 
+# Install MySQL 5.5 if DB=mysql55
+if [[ -n ${DB-} && x$DB =~ ^xmysql55 ]]; then
+  sudo bash .travis_mysql55.sh
+fi
+
 # Install MySQL 5.7 if DB=mysql57
 if [[ -n ${DB-} && x$DB =~ ^xmysql57 ]]; then
   sudo bash .travis_mysql57.sh