CI: Fix shell syntax
diff --git a/circle.yml b/circle.yml
index 116a995..6647c95 100644
--- a/circle.yml
+++ b/circle.yml
@@ -118,8 +118,8 @@
            -u $SAUCE_USERNAME:$SAUCE_ACCESS_KEY \
            -H 'Content-Type: application/json' \
            -d '{
-                 "build": "'$build_name'",
-                 "customData": {"build_url": "'$CIRCLE_BUILD_URL'"}
+                 "build": "'"$build_name"'",
+                 "customData": {"build_url": "'"$CIRCLE_BUILD_URL"'"}
                  "framework": "mocha",
                  "url": "http://localhost:8000/test/unit.html?post_xunit_to=http://localhost:9000",
                  "platforms": [["", "Chrome", ""]]