fixing leadin zero bug

Author: erosb

core/src/main/java/org/everit/json/schema/internal/RelativeJsonPointerFormatValidator.java

@@ -62,7 +62,7 @@ private char curr() {
         }
 
         private void parseUpwardsStepCount() throws ParseException {
-            if (!isDigit(curr())) {
+            if (!isDigit(curr()) || curr() == '0') {
                 fail();
             }
             for (char current = next(); isDigit(current) && pos < input.length(); current = next())

core/src/test/java/org/everit/json/schema/internal/RelativeJsonPointerFormatValidatorTest.java

@@ -75,4 +75,8 @@ public void noUpwardsStepCount() {
         assertFailure("/foo/bar", SUBJECT, "[/foo/bar] is not a valid relative JSON Pointer");
     }
 
+    @Test
+    public void leadingZeroFailure()  {
+        assertFailure("0123", SUBJECT, "[0123] is not a valid relative JSON Pointer");
+    }
 }