Update composer dependencies.

Bump supported version from PHP 5.5.9 to 5.6.0 (based on PHP LTS).
Remove the self-update command.
It apparently wasn't working (the manifest file didn't exist) and is based on a deprecated package.

Author: tomzx

.travis.yml

@@ -1,7 +1,6 @@
 language: php
 
 php:
-    - 5.5
     - 5.6
     - 7.0
     - 7.1

composer.json

@@ -27,17 +27,15 @@
 		}
 	],
 	"require": {
-		"php": ">=5.5.9",
-
-		"herrera-io/phar-update": "^2.0",
+		"php": ">=5.6.0",
 		"klaussilveira/gitter": "dev-php-semver-checker",
-		"symfony/console": "^2.7|^3.0",
+		"symfony/console": "^2.7|^3.0|^4.0",
 		"tomzx/finder": "^0.1",
-		"tomzx/php-semver-checker": "^0.11",
+		"tomzx/php-semver-checker": "^0.12",
 		"vierbergenlars/php-semver": "^3.0"
 	},
 	"require-dev": {
-		"mockery/mockery": "^0.9",
+		"mockery/mockery": "^1.0",
 		"phpunit/phpunit": "^4.0|^5.0"
 	},
 	"bin": [
@@ -55,7 +53,7 @@
 	},
 	"config": {
 		"platform": {
-			"php": "5.5.9"
+			"php": "5.6.0"
 		}
 	},
 	"extra": {