Remove PHP 5.3 support.

5.3 is now [EOL] and there is no reason for us to continue to support
this version from this moment on.  Users needing PHP 5.3 support can use
the previous version.

[EOL]: http://php.net/archive/2014.php#id2014-08-14-1

Author: Spencer Rinehart

.travis.yml

@@ -1,7 +1,7 @@
 language: php
 php:
   - 5.6
-  - 5.3
+  - 5.4
 env:
   - EXT_VERSION=1.3.7 DB_PACKAGE=mongodb-10gen
   - EXT_VERSION=1.3.7 DB_PACKAGE=mongodb-org

composer.json

@@ -21,7 +21,7 @@
     ],
     "license": "MIT",
     "require": {
-        "php": ">=5.3.2",
+        "php": "~5.4",
         "ext-mongo": "~1.3"
     },
     "require-dev": {