CSS example grammar: Simplify |integer| and |float| rules

It's not necessary to parse |parts| in the |integer| and |float| rule
into integer/float value. Everywhere these rules are used the result is
converted back into string anyway.

examples/css.pegjs

@@ -316,10 +316,10 @@ nmchar
   / escape
 
 integer
-  = parts:$[0-9]+ { return parseInt(parts); }
+  = parts:$[0-9]+ { return parts; }
 
 float
-  = parts:$([0-9]* "." [0-9]+) { return parseFloat(parts); }
+  = parts:$([0-9]* "." [0-9]+) { return parts; }
 
 string1
   = '"' chars:([^\n\r\f\\"] / "\\" nl:nl { return nl } / escape)* '"' {