Fixing es-lint problems (#86)

* Fixing es-lint problems

I discovered these by pulling down the project for the first time and running

```bash
npm test
```

I also am ignoring the package-lock.json since it showed up when I ran the following:

```bash
npm install
```

* removing package-lock.json from .gitignore

Author: russellsanborn

Circle.js

@@ -44,6 +44,7 @@ export class ProgressCircle extends Component {
     showsText: PropTypes.bool,
     size: PropTypes.number,
     style: RNViewPropTypes.style,
+    strokeCap: PropTypes.oneOf(['butt', 'square', 'round']),
     textStyle: Text.propTypes.style,
     thickness: PropTypes.number,
     unfilledColor: PropTypes.string,

CircleSnail.js

@@ -32,7 +32,7 @@ export default class CircleSnail extends Component {
     spinDuration: PropTypes.number,
     style: RNViewPropTypes.style,
     thickness: PropTypes.number,
-    strokeCap: PropTypes.string
+    strokeCap: PropTypes.string,
   };
 
   static defaultProps = {
@@ -42,7 +42,7 @@ export default class CircleSnail extends Component {
     hidesWhenStopped: false,
     size: 40,
     thickness: 3,
-    strokeCap: 'round'
+    strokeCap: 'round',
   };
 
   constructor(props) {