Update config.yml

Qinghao Shi · web-flow · commit 0ed6de3ab53b · 2020-04-23T00:25:45.000+01:00
diff --git a/.circleci/config.yml b/.circleci/config.yml
@@ -6,7 +6,7 @@ version: 2
 jobs:
   build:
     docker:
-      - image: mbedos/mbed-os-env:stable
+      - image: mbedos/mbed-os-env@stable
     working_directory: ~
     steps:
       - checkout:
