Corrected `indices.get_warmer` API (index not required, base path just `/_warmer`)

rest-api-spec/api/indices.get_warmer.json

@@ -3,12 +3,11 @@
     "documentation": "http://www.elasticsearch.org/guide/reference/api/admin-indices-warmers/",
     "methods": ["GET"],
     "url": {
-      "path": "/{index}/_warmer",
+      "path": "/_warmer",
       "paths": ["/{index}/_warmer", "/{index}/_warmer/{name}", "/{index}/{type}/_warmer/{name}"],
       "parts": {
         "index": {
           "type" : "list",
-          "required" : true,
           "description" : "A comma-separated list of index names to restrict the operation; use `_all` or empty string to perform the operation on all indices"
         },
         "name": {