README.md: Remove coverity scan badge.

Coverity Scan seems to be broken for this project on Synopsis side and
there is absolutely no way how to contact their support or whatever to
fix it.

See #1

README.md

@@ -1,6 +1,5 @@
 [![Build status (travis-ci.com)](https://img.shields.io/travis/mity/centijson/master.svg?label=linux%20build)](https://travis-ci.org/mity/centijson)
 [![Build status (appveyor.com)](https://img.shields.io/appveyor/ci/mity/centijson/master.svg?label=windows%20build)](https://ci.appveyor.com/project/mity/centijson/branch/master)
-[![Coverity Scan Build Status](https://img.shields.io/coverity/scan/mity-centijson.svg?label=coverity%20scan)](https://scan.coverity.com/projects/mity-centijson)
 [![Codecov](https://img.shields.io/codecov/c/github/mity/centijson/master.svg?label=code%20coverage)](https://codecov.io/github/mity/centijson)
 
 # CentiJSON Readme