phone-number: Clears up contradiction re: why 11 digits is invalid

There are two tests concerning 11 digit numbers.  One test says they are valid when the digits start with one.  The other test states that 11 digits is invalid, but doesn't state why.  The two tests seem to be contradicting each other.

exercises/phone-number/canonical-data.json

@@ -1,6 +1,6 @@
 {
   "exercise": "phone-number",
-  "version": "1.0.1",
+  "version": "1.0.2",
   "cases": [
     {
       "description": "Cleanup user-entered phone numbers",
@@ -35,7 +35,7 @@
           "expected": null
         },
         {
-          "description": "invalid when 11 digits",
+          "description": "invalid when 11 digits does not start with a 1",
           "property": "clean",
           "phrase": "21234567890",
           "expected": null