Escape apostrophe's using entity number (') rather than name (').

The ' entity is an XML entity, rather than an HTML entity, and is not
supported by Internet Explorer. The numeric form is supported in both XML
and HTML.

src/main/java/com/samskivert/mustache/Mustache.java

@@ -640,7 +640,7 @@ public class Mustache
      * need to be applied in order so amps are not double escaped.) */
     protected static final String[][] ATTR_ESCAPES = {
         { "&", "&" },
-        { "'", "'" },
+        { "'", "'" },
         { "\"", """ },
         { "<", "&lt;" },
         { ">", "&gt;" },