fix: semantic-release as optional dependency

.travis.yml

@@ -2,7 +2,7 @@ language: node_js
 node_js:
   # we recommend testing addons with the same minimum supported node version as Ember CLI
   # so that your addon works for all apps
-  - '6'
+  - stable
 
 sudo: false
 dist: trusty
@@ -37,7 +37,7 @@ before_install:
   - export PATH=$HOME/.yarn/bin:$PATH
 
 install:
-  - yarn install --no-lockfile --non-interactive
+  - yarn install --no-lockfile --non-interactive --skip-optional
 
 script:
   - yarn lint:js
@@ -48,8 +48,8 @@ script:
 after_success:
   - nvm install 10
   - nvm use 10
-  - npm install
-  - npm run travis-deploy-once "npm run semantic-release"
+  - yarn install --no-lockfile --non-interactive
+  - yarn travis-deploy-once "npm run semantic-release"
 branches:
   except:
     - /^v\d+\.\d+\.\d+$/

package.json

@@ -22,7 +22,6 @@
   "author": "Mike North <michael.l.north@gmail.com> (http://mike.works)",
   "license": "MIT",
   "devDependencies": {
-    "@mike-north/js-lib-semantic-release-config": "^0.0.0-development",
     "broccoli-asset-rev": "^2.4.6",
     "ember-cli": "^3.3.0",
     "ember-cli-dependency-checker": "^2.1.0",
@@ -47,8 +46,11 @@
     "eslint-plugin-ember": "^5.0.0",
     "eslint-plugin-node": "^5.2.1",
     "loader.js": "^4.2.3",
-    "travis-deploy-once": "^5.0.7",
-    "semantic-release": "^15.9.12"
+    "travis-deploy-once": "^5.0.7"
+  },
+  "optionalDependencies": {
+    "semantic-release": "^15.9.12",
+    "@mike-north/js-lib-semantic-release-config": "^0.0.0-development"
   },
   "keywords": [
     "ember-addon",