fix: improve error message

Author: arlac77

src/step-provider-mixin.js

@@ -17,7 +17,7 @@ export function StepProviderMixin(superclass) {
     declareStep(config, ...args) {
       const factory = this.registeredSteps.get(config.type);
       if (factory === undefined) {
-        throw new Error(`Undefined type ${config.type}`);
+        throw new Error(`Undefined step ${config.type}`);
       }
 
       return new factory(config, ...args);

tests/step-provider-mixin-test.js

@@ -39,6 +39,6 @@ test('provider unknown type', async t => {
       {}
     );
   } catch (e) {
-    t.is(e.message, 'Undefined type unknown-step');
+    t.is(e.message, 'Undefined step unknown-step');
   }
 });