Bump package version in preparation for alpha2 release (#7586)

* Bump package version in preparation for alpha2 release
* Bump lockfile as well
* Mark build as pre-release

.travis.yml

@@ -56,3 +56,4 @@ deploy:
   skip_cleanup: true
   on:
     tags: true
+  tag: next

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "chart.js",
-  "version": "3.0.0-alpha",
+  "version": "3.0.0-alpha.2",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {

package.json

@@ -2,7 +2,7 @@
   "name": "chart.js",
   "homepage": "https://www.chartjs.org",
   "description": "Simple HTML5 charts using the canvas element.",
-  "version": "3.0.0-alpha",
+  "version": "3.0.0-alpha.2",
   "license": "MIT",
   "jsdelivr": "dist/chart.min.js",
   "unpkg": "dist/chart.min.js",