convert.js edits, fixes #11
convert.js edits, fixes #11

Made modifications in the js file to fix the `Cannot read property 'toLowerCase' of undefined` error.
**Usages:**
convert.Metric(1);  // false
convert.Metric(1, "cm");  // false
convert.Metric(1, null, "m")  // false
yakupad/convert.js,ertugrulungor/convert.js,YazilimMuhendisiyizBiz/convert.js