fix lerna version

Author: Feiyang1

package.json

@@ -97,7 +97,7 @@
     "karma-summary-reporter": "1.7.2",
     "karma-webpack": "4.0.2",
     "lcov-result-merger": "3.1.0",
-    "lerna": "^3.20.2",
+    "lerna": "3.20.2",
     "listr": "0.14.3",
     "lodash": "4.17.15",
     "long": "3.2.0",