minor: exp["10"] => exp[10]

lib/compress.js

@@ -2287,6 +2287,12 @@ merge(Compressor.prototype, {
                     property   : prop
                 });
             }
+            var v = parseFloat(prop);
+            if (!isNaN(v) && v.toString() == prop) {
+                self.property = make_node(AST_Number, self.property, {
+                    value: parseFloat(prop)
+                });
+            }
         }
         return self;
     });