fix(striker-ui): export testLength() in barrel

striker-ui/lib/test_input/index.ts

@@ -1,6 +1,7 @@
 import testInput from './testInput';
+import testLength from './testLength';
 import testMax from './testMax';
 import testNotBlank from './testNotBlank';
 import testRange from './testRange';
 
-export { testInput, testMax, testNotBlank, testRange };
+export { testInput, testLength, testMax, testNotBlank, testRange };