Build: Switch PHP 5.2 and 5.3 to Travis' Ubuntu `precise` image

Starting today, Travis will begin switching the default image to `trusty`, which does not support PHP 5.2 or 5.3.

This is not a full fix, because Travis will be dropping `precise` support entirely in September (https://github.com/travis-ci/travis-ci/issues/8072).  However, it buys us some time until then.

Props netweb.
Fixes #41292 for trunk.


git-svn-id: https://develop.svn.wordpress.org/trunk@41072 602fd350-edb4-49c9-b593-d223f7449a82

.travis.yml

@@ -1,4 +1,5 @@
 sudo: false
+dist: trusty
 language: php
 cache:
   apt: true
@@ -22,7 +23,9 @@ matrix:
   - php: 5.5
   - php: 5.4
   - php: 5.3
+    dist: precise
   - php: 5.2
+    dist: precise
   - php: nightly
   allow_failures:
   - php: nightly