Add heading, [fix] exchange 'string' for 'variable'

Author: CristinaSolana

manual/en-US/coding-standards/chapters/javascript.md

@@ -1,12 +1,14 @@
+## JavaScript
+
 ## Naming Conventions
 
 Use descriptive words or terse phrases for names.
 
 Variables and Functions should be camel case, starting with a lowercase letter: `likeThis`
 
-### Strings
+### Variables
 
-**Use names that describe what the string is:**
+**Use names that describe what the variable is:**
 
 `var element = document.getElementById('elementId');`