Update plugins.md (#202)

Author: biggytech

api/plugins.md

@@ -8,6 +8,6 @@
 # Plugin Utilities
 
 The plugin utilities are for those who want to extend Chai with their own set of
-assertions. The [Code Plugin Concepts]({{site.github.url}}/guide/plugins) and
+assertions. The [Core Plugin Concepts]({{site.github.url}}/guide/plugins) and
 [Building a Helper]({{site.github.url}}/guide/helpers) guide tutorials are a great reference on
 how to get started with your own assertions.