chore: add package script to configure examples (#3361)

Because I keep copy/pasting the commands and it is tedious to do so.

.travis.yml

@@ -234,10 +234,7 @@ jobs:
       script:
         # Travis lets scripts continue even if previous steps fail: https://github.com/travis-ci/travis-ci/issues/1066
         - npm run build -- --scope={ipfs-core,ipfs,ipfs-http-client,ipfs-message-port-*} &&
-          rm -rf node_modules packages/*/node_modules &&
-          npx json -I -f ./lerna.json -e "this.packages.push('examples/*')" &&
-          npx json -I -f ./lerna.json -e "this.command.bootstrap.nohoist = ['ipfs-css', 'tachyons']" &&
-          npm install &&
+          npm run configure-examples &&
           npm run test -- --scope=example* --concurrency=1
 
     - stage: release-rc

package.json

@@ -26,13 +26,14 @@
     "clean": "lerna run clean",
     "lint": "lerna run lint",
     "dep-check": "lerna run dep-check",
+    "configure-examples": "run-s release:pre:add-examples release:pre:add-hoisted-modules release:pre:reinstall",
     "release": "run-s release:pre:* release:publish docker:release release:post:*",
     "release:pre:non-dirty-repo": "git diff --quiet",
     "release:pre:update-contributors": "aegir release --lint=false --test=false --bump=false --build=false --changelog=false --commit=false --tag=false --push=false --ghrelease=false --docs=false --publish=false",
     "release:pre:ignore-changes-to-lerna-config": "git update-index --assume-unchanged ./lerna.json",
     "release:pre:build": "NODE_ENV=production npm run build -- --scope={ipfs-core,ipfs,ipfs-http-client,ipfs-message-port-*}",
-    "release:pre:add-examples": "json -I -f ./lerna.json -e \"this.packages.push('examples/*')\"",
-    "release:pre:add-hoisted-modules": "json -I -f ./lerna.json -e \"this.command.bootstrap.nohoist = ['ipfs-css', 'tachyons']\"",
+    "release:pre:add-examples": "json -I -f ./lerna.json -e \"this.packages.push('examples/*'); this.packages = [...new Set(this.packages)]\"",
+    "release:pre:add-hoisted-modules": "json -I -f ./lerna.json -e \"this.command.bootstrap.nohoist = ['ipfs-css', 'tachyons']; this.command.bootstrap.nohoist = [...new Set(this.command.bootstrap.nohoist)]\"",
     "release:pre:reinstall": "rm -rf node_modules */*/node_modules package-lock.json */*/package-lock.json && npm i && rm -rf package-lock.json */*/package-lock.json",
     "release:publish": "lerna publish",
     "docker:release": "run-s docker:release:*",