fix(themes): add missing 0 border width

Author: brandyscarney

core/src/themes/base/default.tokens.ts

@@ -87,6 +87,7 @@ export const defaultTheme: DefaultTheme = {
   },
 
   borderWidth: {
+    0: '0',
     25: '1px',
     50: '2px',
     75: '3px',