PARQUET-13: The `-d` option for `parquet-schema` shouldn't have optional argument

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #11 from liancheng/fix-cli-arg and squashes the following commits:

85a5453 [Cheng Lian] Reverted the dummy change
47ce817 [Cheng Lian] Dummy change to trigger Travis
1c0a244 [Cheng Lian] The `-d` option for `parquet-schema` shouldn't have optional argument