remove maven-badges.herokuapp.com from readme
remove maven-badges.herokuapp.com from readme

Fixes #3090

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=191298096

mosoft521/guava,typetools/guava,mosoft521/guava,rgoldberg/guava,rgoldberg/guava,EdwardLee03/guava,mosoft521/guava,xasx/guava,typetools/guava,google/guava,google/guava,google/guava,EdwardLee03/guava,xasx/guava