fix: Fix UglifyJs error during Angular CLI prod build (#47)

Author: dtopalov

src/dates/date-pattern.js

@@ -11,10 +11,10 @@ const SHORT_MORE_PENALTY_DELTA = 1;
 const LONG_MORE_PENALTY_DELTA = 2;
 
 const PENALTIES = {
-    [LONG_LESS_PENALTY_DELTA]: 8,
-    [SHORT_LESS_PENALTY_DELTA]: 6,
-    [LONG_MORE_PENALTY_DELTA]: 6,
-    [SHORT_MORE_PENALTY_DELTA]: 3
+    [LONG_LESS_PENALTY_DELTA.toString()]: 8,
+    [SHORT_LESS_PENALTY_DELTA.toString()]: 6,
+    [LONG_MORE_PENALTY_DELTA.toString()]: 6,
+    [SHORT_MORE_PENALTY_DELTA.toString()]: 3
 };
 
 const VALUE_FORMAT_LENGTH = {