Do not pull unneeded dependencies

Author: gjuric

composer.json

@@ -14,16 +14,20 @@
         "php": ">=5.4",
         "php-http/httplug": "^1.0",
         "php-http/message-factory": "^1.0.2",
-        "psr/log": "^1.0",
-        "psr/cache": "^1.0",
         "php-http/client-common": "^1.0",
         "php-http/message": "^1.0",
         "symfony/options-resolver": "^2.6|^3.0"
     },
     "require-dev": {
         "symfony/stopwatch": "^2.3",
         "phpspec/phpspec": "^2.4",
-        "henrikbjorn/phpspec-code-coverage" : "^1.0"
+        "henrikbjorn/phpspec-code-coverage" : "^1.0",
+        "psr/log": "^1.0",
+        "psr/cache": "^1.0"
+    },
+    "conflict": {
+        "psr/log": ">= 2.0.0",
+        "psr/cache": ">= 2.0.0"
     },
     "autoload": {
         "psr-4": {