further loosen composer dependencies, and fix monolog dependency (ErrorHandler was not available until 1.6.0)

Author: abacaphiliac

composer.json

@@ -14,22 +14,22 @@
         }
     ],
     "require": {
-        "monolog/monolog": "1.*",
+        "monolog/monolog": "^1.6",
         "php": ">=5.5",
-        "psr/log": "1.0.*"
+        "psr/log": "^1.0"
     },
     "require-dev": {
         "guzzlehttp/guzzle": "^6.2.1",
         "kevinrob/guzzle-cache-middleware": "^1.4.1",
         "phpunit/phpunit": ">=4.8.26 <5.4",
-        "phpdocumentor/phpdocumentor": "2.*",
-        "predis/predis": "1.0.*",
-        "zendframework/zend-serializer": "2.7.*"
+        "phpdocumentor/phpdocumentor": "^2.0",
+        "predis/predis": "^1.0",
+        "zendframework/zend-serializer": "^2.7"
     },
     "suggested": {
         "guzzlehttp/guzzle": "^6.2.1",
         "kevinrob/guzzle-cache-middleware": "^1.4.1",
-        "predis/predis": "1.0.*"
+        "predis/predis": "^1.0"
     },
     "autoload": {
         "psr-4": {