Fix typo

Author: U-FAREAST\ramgupt

src/main/java/com/microsoft/graph/concurrency/DefaultExecutors.java

@@ -145,7 +145,7 @@ public ILogger getLogger() {
         return logger;
     }
 
-    public void shutDownBackgroundExecutors() {
+    public void shutdownBackgroundExecutors() {
     	this.backgroundExecutor.shutdown();
     }
 }

src/main/java/com/microsoft/graph/concurrency/IExecutors.java

@@ -71,5 +71,5 @@ <Result> void performOnForeground(final ClientException exception,
     /**
      * Shuts down the background executors
      */
-    void shutDownBackgroundExecutors();
+    void shutdownBackgroundExecutors();
 }

src/main/java/com/microsoft/graph/core/BaseClient.java

@@ -174,7 +174,7 @@ public void setSerializer(final ISerializer serializer) {
         this.serializer = serializer;
     }
 
-    public void shutDown() {
-    	this.executors.shutDownBackgroundExecutors();
+    public void shutdown() {
+    	this.executors.shutdownBackgroundExecutors();
     }
 }

src/main/java/com/microsoft/graph/core/IBaseClient.java

@@ -90,5 +90,5 @@ public interface IBaseClient {
     /*
      * Shuts down the executors.
      */
-    void shutDown();
+    void shutdown();
 }