Updated key

Changing all samples to reflect standard naming.
<SERVICE>_SUBSCRIPTION_KEY

Author: wiazur

Search/BingEntitySearch/src/main/java/com/microsoft/azure/cognitiveservices/search/entitysearch/samples/BingEntitySearchSample.java

@@ -273,7 +273,7 @@ public static void main(String[] args) {
             // If not, you may get an API key not found exception.
             // IMPORTANT: if you have not set the `AZURE_BING_SAMPLES_API_KEY` environment variable to your cognitive services API key:
             // 1. comment out the below line
-            final String subscriptionKey = System.getenv("AZURE_BING_SAMPLES_API_KEY");
+            final String subscriptionKey = System.getenv("BING_ENTITY_SEARCH_SUBSCRIPTION_KEY");
             // 2. paste your cognitive services API key below, and uncomment the line
             //final String subscriptionKey = "enter your key here";