refactor: Use ServerlessError in pipenv

Author: pgrzesik

lib/pipenv.js

@@ -42,8 +42,9 @@ async function pipfileToRequirements() {
         e.stderrBuffer &&
         e.stderrBuffer.toString().includes('command not found')
       ) {
-        throw new Error(
-          `pipenv not found! Install it with 'pip install pipenv'.`
+        throw new this.serverless.classes.Error(
+          `pipenv not found! Install it according to the poetry docs.`,
+          'PYTHON_REQUIREMENTS_PIPENV_NOT_FOUND'
         );
       }
       throw e;