fixing lint issue from https://github.com/topcoder-platform/topcoder-react-ui-kit/pull/11/files

Author: sushilshinde

src/styles/_mixins/variables.scss

@@ -36,6 +36,7 @@ $tc-gray-neutral-light: #fafafb;
 $tc-white: #fff;
 
 /* Accents & Shades. */
+$tc-dark-blue-120: #006ad7;
 $tc-dark-blue-110: #006dea;
 $tc-dark-blue-100: #0681ff;
 $tc-dark-blue-70: #55a5ff;