Fix a problem with package.json version after release (#203)

Author: patrick-tolosa

.release-it.json

@@ -0,0 +1,7 @@
+{
+  "plugins": {
+    "@release-it/bumper": {
+      "out": ["package.json", "../package.json"]
+    }
+  }
+}

package.json

@@ -29,6 +29,7 @@
     "@babel/cli": "^7.8.4",
     "@babel/core": "^7.9.0",
     "@babel/preset-env": "^7.9.0",
+    "@release-it/bumper": "^2.0.0",
     "@rollup/plugin-node-resolve": "^7.1.1",
     "@types/jest": "^25.2.3",
     "@types/mock-fs": "^4.10.0",