fix: error on isError due to changes of output format of npm view (#21)

Author: sotarok

Diff for: lib/can-npm-publish.js

@@ -108,7 +108,7 @@ const viewPackage = (packageName, registry, options) => {
             };
         };
         const isError = (json) => {
-            return json && "error" in json;
+            return json && typeof json !== "string" && "error" in json;
         };
         const is404Error = (json) => {
             return isError(json) && json.error.code === "E404";