Parse numeric strings as numbers (#902)

* Parse numeric strings as numbers

* Additionally check for type of field value

Author: ekzyis

components/form.js

@@ -450,7 +450,9 @@ function InputInner ({
       if (draft) {
         // for some reason we have to turn off validation to get formik to
         // not assume this is invalid
-        helpers.setValue(draft, false)
+        const isNumeric = /^[0-9]+$/.test(draft)
+        const numericExpected = typeof field.value === 'number'
+        helpers.setValue(isNumeric && numericExpected ? parseInt(draft) : draft, false)
         onChange && onChange(formik, { target: { value: draft } })
       }
     }