refactor(dateFilter): improve readability on conditional assignment

Use ternary operator instead of if statement

Closes angular#5065

Author: dimirc

src/ng/filter/filters.js

@@ -442,11 +442,7 @@ function dateFilter($locale) {
     format = format || 'mediumDate';
     format = $locale.DATETIME_FORMATS[format] || format;
     if (isString(date)) {
-      if (NUMBER_STRING.test(date)) {
-        date = int(date);
-      } else {
-        date = jsonStringToDate(date);
-      }
+      date = NUMBER_STRING.test(date) ? int(date) : jsonStringToDate(date);
     }
 
     if (isNumber(date)) {