MDL-55835 eslint: bump to v3.7.1
1) Bump eslint verson in npm
2) Enable tabs rule introduced in 3.2.0
3) With rules deprecated in 3.3.0 to their replacements
http://eslint.org/blog/2016/08/eslint-v3.3.0-released
4) Deprecate the use of M.str (fixes MDLSITE-3646) with new
no-restricted-properties introduced in 3.5.0
5) Fixup no-unused-vars - remove argsIgnorePattern which shouldn't have allowed
partial matches and turns out to be uncesssary
(detected because of https://github.com/eslint/eslint/issues/7250 in 3.6.0)