docs(storage): fix minor typo in code docs (#6485)

Author: Salakar

FirebaseStorage/Sources/FIRStorageTask_Private.h

@@ -50,7 +50,7 @@ NS_ASSUME_NONNULL_BEGIN
 @property(strong, nonatomic, nullable) NSError *error;
 
 /**
- * NSProgress object which tracks the progess of an observable task.
+ * NSProgress object which tracks the progress of an observable task.
  */
 @property(strong, nonatomic) NSProgress *progress;
 

FirebaseStorage/Sources/Public/FirebaseStorage/FIRStorageTaskSnapshot.h

@@ -48,7 +48,7 @@ NS_SWIFT_NAME(StorageTaskSnapshot)
 @property(readonly, copy, nonatomic) FIRStorageReference *reference;
 
 /**
- * NSProgress object which tracks the progess of an upload or download.
+ * NSProgress object which tracks the progress of an upload or download.
  */
 @property(readonly, strong, nonatomic, nullable) NSProgress *progress;