Fixed case-insensitive issue in a few corpuses.
Fixed case-insensitive issue in a few corpuses.

Fixed issue with every column being dropped when doing case-insensitive queries in the German, Chinese, and Hebrew corpuses.

This is my solution to [Issue 6](https://github.com/econpy/google-ngrams/issues/6).
econpy/google-ngrams,rjonczy/google-ngrams