Fix Typo in FourMzTextInputFormat #30

Hi, there's a typo in FourMzTextInputFormat where it extends from the wrong class: Mc should be Mz.

#27 Fixes this problem, but it hasn't been merged yet for some reason since October. There's also the issue of the wrong extends:

• FourMcTextInputFormat should extend from FourMcInputFormat<LongWritable, Text> instead of just FourMcInputFormat.
• Same thing applies to FourMzTextInputFormat.