build: revise travis setup

Author: Chris Armstrong

.travis.yml

@@ -1,6 +1,8 @@
 language: node_js
 node_js:
+  - '8'
   - '10'
+  - '12'
 
 sudo: false
 
@@ -12,7 +14,7 @@ before_install:
 
 install:
   - npm install --save-dev serverless-offline
-  - npm install -g serverless@^1
+  - npm install --save-dev serverless@^1
   - npm install aws-sdk
   - npm install --save dynamodb-doc-client-wrapper
   - serverless create --template aws-nodejs
@@ -25,19 +27,15 @@ install:
   - sed -i '18 a plugins:' serverless.yml
   - sed -i '19 a - serverless-offline' serverless.yml
   - sed -i '20 a - serverless-dynamodb-local' serverless.yml
+  - "sed -i '21 a custom: { dynamodb: { stages: [dev] } }'"
   - cd ..
   - cd ..
-  - npm install --save-dev mocha
-  - npm install --save-dev should
-  - npm install --save expect
-  - npm install --save request
-  - npm install --save chai
   - travis_retry npm install
   - cd test/sample-template
 
 before_script:
   - sls dynamodb install
-  - sls offline start &
+  - sls offline start --stage dev &
   - sleep 15
   - cd ..
   - cd ..