Docs: Fix various spelling errors

Closes gh-2761

src/deferred.js

@@ -135,7 +135,7 @@ jQuery.extend( {
 									// Handle all other returned values
 									} else {
 
-										// Only substitue handlers pass on context
+										// Only substitute handlers pass on context
 										// and multiple values (non-spec behavior)
 										if ( handler !== Identity ) {
 											that = undefined;