Fix problem in version detection via js variables (#2033)

* Fix version detection in js variables (webextension)

* Fix version detection in js variables (NPM)

src/drivers/npm/driver.js

@@ -246,7 +246,7 @@ class Driver {
             return parent && parent.hasOwnProperty(property) ? parent[property] : null;
           }, browser.window);
 
-          value = typeof value === 'string' ? value : !!value;
+          value = typeof value === 'string' || typeof value === 'number' ? value : !!value;
 
           if ( value ) {
             js[appName][chain][index] = value;

src/drivers/webextension/js/inject.js

@@ -53,7 +53,7 @@
         }
       }
 
-      return typeof value === 'string' ? value : !!value;
+      return typeof value === 'string' || typeof value === 'number' ? value : !!value;
     } catch(e) {
       // Fail quietly
     }