fix markdown code

Author: morapet

README.md

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-# Synergy Core https://ci.appveyor.com/api/projects/status/s35ibcrsd9bvo4r7?svg=true
+# Synergy Core [![Build status](https://ci.appveyor.com/api/projects/status/s35ibcrsd9bvo4r7/branch/master?svg=true)](https://ci.appveyor.com/project/morapet/synergy-core/branch/master)
+
 
 This is the open source core component of Synergy, a keyboard and mouse sharing tool.