TEST: update example.json file

Author: Qinghao Shi

tools/test/examples/examples.json

@@ -471,7 +471,7 @@
         "test-repo-source": "github",
         "features" : [],
         "targets" : ["K64F"],
-        "toolchains" : [],
+        "toolchains" : ["GCC_ARM"],
         "exporters": [],
         "compile" : true,
         "export": true,