docs(quickstart): Change Npm to npm (#2398)

Author: techeverri

public/docs/js/latest/quickstart.jade

@@ -460,7 +460,7 @@ code-example(format="").
 .l-main-section
 :marked
   <a id="npm-errors"></a>
-  ### Appendix: Npm errors and warnings
+  ### Appendix: npm errors and warnings
 
   All is well if there are no console messages starting with `npm ERR!` *at the end* of **npm install**. 
   There might be a few `npm WARN` messages along the way &mdash; and that is perfectly fine.