[libpng16] Change "n bit" to "n-bit" in comments.

contrib/libtests/fakepng.c

@@ -1,4 +1,12 @@
 /* Fake a PNG - just write it out directly. */
+ *
+ * COPYRIGHT: Written by John Cunningham Bowler, 2014.
+ * To the extent possible under law, the author has waived all copyright and
+ * related or neighboring rights to this work.  This work is published from:
+ * United States.
+ *
+ */
+
 #include <stdio.h>
 #include <zlib.h> /* for crc32 */