fix: proptypes for breakpoints (#70)

Author: aaronvanston

src/components/Col/Col.js

@@ -41,10 +41,10 @@ Col.defaultProps = {
 export const alignSelfOptions = ['auto', 'flex-start', 'flex-end', 'center', 'baseline', 'stretch'];
 
 Col.propTypes = {
-  xs: PropTypes.oneOfType([PropTypes.number, PropTypes.oneOf(['hidden, auto'])]),
-  sm: PropTypes.oneOfType([PropTypes.number, PropTypes.oneOf(['hidden, auto'])]),
-  md: PropTypes.oneOfType([PropTypes.number, PropTypes.oneOf(['hidden, auto'])]),
-  lg: PropTypes.oneOfType([PropTypes.number, PropTypes.oneOf(['hidden, auto'])]),
+  xs: PropTypes.oneOfType([PropTypes.number, PropTypes.oneOf(['hidden', 'auto'])]),
+  sm: PropTypes.oneOfType([PropTypes.number, PropTypes.oneOf(['hidden', 'auto'])]),
+  md: PropTypes.oneOfType([PropTypes.number, PropTypes.oneOf(['hidden', 'auto'])]),
+  lg: PropTypes.oneOfType([PropTypes.number, PropTypes.oneOf(['hidden', 'auto'])]),
 
   gutter: PropTypes.oneOfType([
     PropTypes.number,