Modifies composer.json dependency on php to >= 5.4.0 for acquia#54

PHP 5.4 is the minimum requirement for the following:

- guzzle 5.2.0
- ringphp 1.0.7
- streams 3.0.0
- phploc 2.1.1
- promise v2.2.0

    $ find vendor -name composer.json -exec grep -o ".\bphp\b.:.*" {} \; | sort -u
    "php": ">=5.2.3"
    "php": ">=5.3",
    "php": ">=5.3.0"
    "php": ">=5.3.0",
    "php": ">=5.3.2"
    "php": ">=5.3.2",
    "php": ">=5.3.3"
    "php": ">=5.3.3",
    "php": ">=5.4",
    "php": ">=5.4.0"
    "php": ">=5.4.0",

    $ find vendor -name composer.json -exec grep -H ".\bphp\b.:.*5\.4" {} \; | sort -u
    vendor/guzzlehttp/guzzle/composer.json:        "php": ">=5.4.0",
    vendor/guzzlehttp/ringphp/composer.json:        "php": ">=5.4.0",
    vendor/guzzlehttp/streams/composer.json:        "php": ">=5.4.0"
    vendor/phploc/phploc/composer.json:        "php": ">=5.4",
    vendor/react/promise/composer.json:        "php": ">=5.4.0"

This commit also removes the php 5.3 test environment from Travis CI.

.travis.yml

@@ -4,7 +4,6 @@ php:
   - 5.6
   - 5.5
   - 5.4
-  - 5.3
   - hhvm
 
 before_script:

composer.json

@@ -12,7 +12,7 @@
         }
     ],
     "require": {
-        "php": ">=5.3.0",
+        "php": ">=5.4.0",
         "cpliakas/psolr": ">=0.4",
         "guzzlehttp/guzzle": "~5.0",
         "guzzle/service": "~3.0",