Minor PHP 7.4 corrections (#89)

Author: drbyte

README.md

@@ -105,7 +105,7 @@ wskdev fresh -t local-php
 To use as docker action push to your own dockerhub account
 ```
 docker tag whisk/php7.4Action $user_prefix/action-php-v7.4
-docker push $user_prefix/action-php-v7.3
+docker push $user_prefix/action-php-v7.4
 ```
 ```
 docker tag whisk/php7.3Action $user_prefix/action-php-v7.3

core/php7.4Action/composer.json

@@ -1,7 +1,7 @@
 {
     "config": {
         "platform": {
-            "php": "7.3"
+            "php": "7.4"
         }
     },
     "require": {