Updated key

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

Author: wiazur

Search/BingCustomSearch/src/main/java/com/microsoft/azure/cognitiveservices/search/customsearch/samples/BingCustomSearchSample.java

@@ -76,7 +76,7 @@ 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` and AZURE_BING_SAMPLES_CUSTOM_CONFIG_ID environment variables to your cognitive services API key:
             // 1. comment out the below lines
-            final String subscriptionKey = System.getenv("AZURE_BING_SAMPLES_API_KEY");
+            final String subscriptionKey = System.getenv("BING_CUSTOM_SEARCH_SUBSCRIPTION_KEY");
             final String customConfigId = System.getenv("AZURE_BING_SAMPLES_CUSTOM_CONFIG_ID");
             // 2. paste your cognitive services API key and custom config id below, and uncomment the following two lines
             //final String subscriptionKey = "enter your key here";