Give logger public access

Resolves #42

Author: cbales

graphsdk/src/main/java/com/microsoft/graph/extensions/GraphServiceClient.java

@@ -87,7 +87,7 @@ public Builder executors(final IExecutors executors) {
          * @param logger The logger
          * @return the instance of this builder
          */
-        private Builder logger(final ILogger logger) {
+        public Builder logger(final ILogger logger) {
             mClient.setLogger(logger);
             return this;
         }