Cache badges
Cache badges

- use google's caching proxy for img.shields.io badges
- fixes #2805
gojomo/gensim,gojomo/gensim,piskvorky/gensim,gojomo/gensim,RaRe-Technologies/gensim,gojomo/gensim,RaRe-Technologies/gensim,RaRe-Technologies/gensim,RaRe-Technologies/gensim,piskvorky/gensim,piskvorky/gensim