feat: TS v4, tslint -> eslint, add cspell support (#240)

Update all dependencies, migrate from tslint (deprecated) to typescript-eslint, and add support for
cspell.

BREAKING CHANGE: migrated from tslint (deprecated) to eslint.

.circleci/config.yml

@@ -4,7 +4,6 @@ jobs:
   'node-10':
     docker:
       - image: circleci/node:10
-    working_directory: ~/typescript-starter
     steps:
       - checkout
       # Download and cache dependencies
@@ -21,10 +20,26 @@ jobs:
       - run: npm test
       - run: npm run cov:send
       - run: npm run cov:check
+  'node-12':
+    docker:
+      - image: circleci/node:12
+    steps:
+      - checkout
+      - restore_cache:
+          keys:
+            - v1-dependencies-{{ checksum "package.json" }}
+            - v1-dependencies-
+      - run: npm install
+      - save_cache:
+          paths:
+            - node_modules
+          key: v1-dependencies-{{ checksum "package.json" }}
+      - run: npm test
+      - run: npm run cov:send
+      - run: npm run cov:check
   'node-latest':
     docker:
       - image: circleci/node:latest
-    working_directory: ~/typescript-starter
     steps:
       - checkout
       - restore_cache:
@@ -45,4 +60,5 @@ workflows:
   build:
     jobs:
       - 'node-10'
+      - 'node-12'
       - 'node-latest'