Convert PFFile.isDirty to a property.

Author: nlutsenko

Parse/PFFile.h

@@ -145,7 +145,7 @@ NS_ASSUME_NONNULL_BEGIN
 /*!
  @abstract Whether the file has been uploaded for the first time.
  */
-@property (nonatomic, assign, readonly) BOOL isDirty;
+@property (nonatomic, assign, readonly, getter=isDirty) BOOL dirty;
 
 ///--------------------------------------
 /// @name Storing Data with Parse

Parse/PFFile.m

@@ -37,7 +37,6 @@ @interface PFFile () {
 
 @property (nonatomic, strong, readwrite) PFFileState *state;
 @property (nonatomic, copy, readonly) NSString *stagedFilePath;
-@property (nonatomic, assign, readonly, getter=isDirty) BOOL dirty;
 
 //
 // Private