Resolved review comments

# Spelling mistake in MSAuthenticationProvider
# Added stub for MSGraphMiddleware's setNext method in MSURLSessionManager and Unit test for the same

Author: Vikas Dadheech

MSGraphCoreSDK/MSGraphCoreSDK/Authentication/MSAuthenticationProvider.h

@@ -14,7 +14,7 @@ typedef void(^MSAuthenticationCompletion)(NSMutableURLRequest *request, NSError
 @protocol MSAuthenticationProvider <NSObject>
 
 /**
- Gets the access token. This method should be implmented by a class which should provide the capability of providing the access token.
+ Gets the access token. This method should be implemented by a class which should provide the capability of providing the access token.
  @param completion The completion handler to be called when access token or an error can be returned.
  */
 

MSGraphCoreSDK/MSGraphCoreSDK/Middleware/Implementations/HTTPProvider/MSURLSessionManager.m

@@ -243,11 +243,7 @@ - (void)execute:(MSURLSessionTask *)task withCompletionHandler:(HTTPRequestCompl
 
 - (void)setNext:(id<MSGraphMiddleware>)nextMiddleware
 {
-    if(_nextMiddleware)
-    {
-        [nextMiddleware setNext:_nextMiddleware];
-    }
-    _nextMiddleware = nextMiddleware;
+    NSAssert(NO, @"This class is last node of middleware chain. So can not set any next middleware after this.");
 }
 
 @end

MSGraphCoreSDK/MSGraphCoreSDKTests/Middleware/Implementations/MSURLSessionManagerTests.m

@@ -234,11 +234,7 @@ - (void)testWillPerformRedirect {
 
 - (void)testSetNext{
     id<MSGraphMiddleware> tempMiddleware = OCMProtocolMock(@protocol(MSGraphMiddleware));
-    [_sessionManager setNext:tempMiddleware];
-    XCTAssertEqualObjects(tempMiddleware, _sessionManager.nextMiddleware);
-    id<MSGraphMiddleware> tempMiddleware1 = OCMProtocolMock(@protocol(MSGraphMiddleware));
-    [_sessionManager setNext:tempMiddleware1];
-    XCTAssertEqualObjects(_sessionManager.nextMiddleware, tempMiddleware1);
+    XCTAssertThrows([_sessionManager setNext:tempMiddleware]);
 }
 
 #pragma mark - Middleware execution