Fix prototype function pollution

Fixes #53 per MadsAppvice

lib/index.js

@@ -23,16 +23,16 @@ exports.parseAll = function ( chtml ) {
 	const arr = keys.map( ( key ) => exports.metadataFunctions[ key ]( chtml ) );
 
 	let result; // Result in for loop over results
-	let key; // Key corrsponding to location of result
+	let key; // Key corresponding to location of result
 	return BBPromise.all( arr.map( ( x ) => x.reflect() ) )
 		.then( ( results ) => {
-			for ( const r in results ) {
+			Object.keys( results ).forEach( function ( r ) {
 				result = results[ r ];
 				key = keys[ r ];
 				if ( result && result.isFulfilled() && result.value() ) {
 					meta[ key ] = result.value();
 				}
-			}
+			} );
 			if ( Object.keys( meta ).length === 0 ) {
 				throw new Error( 'No metadata found in page' );
 			}