Fix discourse logo

Author: blegat

README.md

@@ -3,7 +3,7 @@
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 | [![][docs-stable-img]][docs-stable-url] | [![][pkg-0.5-img]][pkg-0.5-url] | [![Build Status][build-img]][build-url] [![Build Status][winbuild-img]][winbuild-url] | [![Gitter][gitter-img]][gitter-url] |
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+| [![][docs-latest-img]][docs-latest-url] | [![][pkg-0.6-img]][pkg-0.6-url] | [![Coveralls branch][coveralls-img]][coveralls-url] [![Codecov branch][codecov-img]][codecov-url] | [<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/a/af/Discourse_logo.png/799px-Discourse_logo.png" width="64">][discourse-url] |
 
 This package provides an interface for manipulating multivariate polynomials.
 Implementing algorithms on polynomials using this interface will allow the algorithm to work for all polynomials implementing the interface.