adding node 10 and force npm 6 or higher

Author: kiwiupover

.travis.yml

@@ -3,6 +3,7 @@ language: node_js
 node_js:
   - "6"
   - "8"
+  - "10"
 
 branches:
   only:
@@ -30,5 +31,6 @@ cache:
   yarn: false # switch to yarn once ember-cli-addon-tests is removed
 
 before_install:
-  - npm config set spin false
-  - npm install -g npm@4
+
+  # TODO: remove when we stop testing against node 6
+  - if [[ `npm -v` < 6* ]]; then npm i -g npm@6; fi

yarn.lock

@@ -2639,7 +2639,7 @@ ember-ajax@^3.1.0:
 
 "ember-cli-addon-tests@github:kiwiupover/ember-cli-addon-tests#test-against-ember-data-release":
   version "0.11.0"
-  resolved "https://codeload.github.com/kiwiupover/ember-cli-addon-tests/tar.gz/d8a352fcf73270ee132f19a7cec7e66095aea330"
+  resolved "https://codeload.github.com/kiwiupover/ember-cli-addon-tests/tar.gz/207d5154f0b662799424e103fc56e97ff7465795"
   dependencies:
     chalk "^2.0.1"
     debug "^3.0.0"