Don't transform when a property name is an integer

An error (`TypeError: Value needs to be a string`) was raised when a
property name was an integer (`obj[10]`).

I don't know if it's the best way to check if we can transform or not a
property. Currently I check if `node.property.value` is not a number.
Should I check `startToken.type === 'Numeric'` instead?
Merge branch 'fix-prop-int' of https://github.com/kewah/esformatter-dot-notation into kewah-fix-prop-int

* 'fix-prop-int' of https://github.com/kewah/esformatter-dot-notation:
  Don't transform when a property name is an integer
Coerce value to be a string

- Will now not convert integers to literal expressions correctly
- Relates to PR #1
Merge branch 'kewah-fix-prop-int'

* kewah-fix-prop-int:
  Coerce value to be a string
  Don't transform when a property name is an integer
0.2.0