Update .gitattributes for GitHub language recognizition as Python

[martinvonk]

I saw that a lot of strange languages were detected by GitHub linguist because of the extensions of certain data files. This removes the languages that aren't on the repository such that python is the main language. This makes pyemu more easily findable on GitHub.

Current languages found:

With new .gitattributes file:

64.77%  Python
35.23%  Jupyter Notebook

[coveralls]

coverage: 79.625% (+0.2%) from 79.433%
when pulling 214fa58 on martinvonk:linguist
into 459eda8 on pypest:develop.

[mnfienen]

thanks @martinvonk - nice addition :)

[martinvonk]

Weirdly enough, there are still two other languages recognized.

I ran github-linguist locally and there these two languages aren't picked up.

I don't know if you have power over the develop branch @mnfienen. But if you have, maybe you can add these two lines:

*.arr linguist-vendored # ignore because recognized as Pyret
*.mps linguist-vendored # ignore because recognized as JetBrains MPS

Otherwise, I can make a new pr.

[martinvonk]

Comment above fixed in #551