Fix up duplicate arg name

'text1' was being used as an arg name twice.

Author: dmaclach

objectivec/DiffMatchPatch.h

@@ -156,7 +156,7 @@ typedef enum {
 - (NSMutableArray *)diff_mainOfOldString:(NSString *)text1 andNewString:(NSString *)text2 checkLines:(BOOL)checklines deadline:(NSTimeInterval)deadline;
 - (NSMutableArray *)diff_computeFromOldString:(NSString *)text1 andNewString:(NSString *)text2 checkLines:(BOOL)checklines deadline:(NSTimeInterval)deadline;
 - (NSMutableArray *)diff_lineModeFromOldString:(NSString *)text1 andNewString:(NSString *)text2 deadline:(NSTimeInterval)deadline;
-- (NSArray *)diff_linesToCharsForFirstString:(NSString *)text1 andSecondString:(NSString *)text1;
+- (NSArray *)diff_linesToCharsForFirstString:(NSString *)text1 andSecondString:(NSString *)text2;
 - (void)diff_chars:(NSArray *)diffs toLines:(NSMutableArray *)lineArray;
 - (NSMutableArray *)diff_bisectOfOldString:(NSString *)text1 andNewString:(NSString *)text2 deadline:(NSTimeInterval)deadline;
 - (NSMutableArray *)diff_bisectSplitOfOldString:(NSString *)text1 andNewString:(NSString *)text2 x:(NSUInteger)x y:(NSUInteger)y deadline:(NSTimeInterval)deadline;