(pub): automatically tag releases as v0.3.x

- by default, NPM uses the "latest" tag, which causes some confusion
  for package maintainers and users alike (c.f. #18)
- using any tag will mean it won't be tagged as latest anymore, so
  just giving the v0.3.x branch the tag v0.3.x should resolve this
  issue

Author: agilgur5

package.json

@@ -1,6 +1,9 @@
 {
   "name": "react-signature-canvas",
   "version": "0.3.0",
+  "publishConfig": {
+    "tag": "v0.3.x"
+  },
   "description": "A signature pad implementation in React",
   "main": "build/index.js",
   "scripts": {