Update FIRAuthDataResult_Internal.h (#3077)

Author: Chuan Ren

Firebase/Auth/Source/Auth/FIRAuthDataResult_Internal.h

@@ -23,7 +23,7 @@ NS_ASSUME_NONNULL_BEGIN
 @interface FIRAuthDataResult () <NSSecureCoding>
 
 /** @property credential
-    @brief The updated OAuth credential after the the sign-in, link and reauthenticate action.
+    @brief The updated OAuth credential after the sign-in, link and reauthenticate action.
     @detail This property is for OAuth sign in only.
  */
 @property(nonatomic, readonly, nullable) FIROAuthCredential *credential;