Merge pull request #3 from ruby/fix-unknown-type-error

Fix unknown type error

Author: hsbt

.gitignore

@@ -1,3 +1,4 @@
 __tests__/runner/*
 node_modules
 package-lock.json
+lib

src/main.ts

@@ -11,7 +11,11 @@ async function run() {
 
     await webhook.send(payload);
   } catch (error) {
-    core.setFailed(error.message);
+    if(error instanceof Error) {
+      core.setFailed(error.message);
+    } else {
+      core.setFailed("Unexpected error");
+    }
   }
 }