build: nodejs v8 and up

BREAKING CHANGE:

Only NodeJS v8 and greater are now supported

.travis.yml

@@ -47,26 +47,26 @@ jobs:
         - npm run lint-docs
         - npm run test-typings
     - stage: test
-      node_js: '6'
+      node_js: '8'
       env: DIALECT=sqlite TSC=true
     - stage: test
-      node_js: '6'
+      node_js: '8'
       sudo: required
       env: MARIADB_VER=mariadb-103 SEQ_MARIADB_PORT=8960 DIALECT=mariadb
     - stage: test
-      node_js: '6'
+      node_js: '8'
       sudo: required
       env: MYSQL_VER=mysql-57 SEQ_MYSQL_PORT=8980 DIALECT=mysql
     - stage: test
-      node_js: '6'
+      node_js: '8'
       sudo: required
       env: POSTGRES_VER=postgres-10 SEQ_PG_PORT=8991 DIALECT=postgres
     - stage: test
-      node_js: '6'
+      node_js: '8'
       sudo: required
       env: POSTGRES_VER=postgres-95 SEQ_PG_PORT=8990 DIALECT=postgres-native
     - stage: release
-      node_js: '8'
+      node_js: '10'
       script:
         - npm run semantic-release
       before_deploy:

appveyor.yml

@@ -10,7 +10,7 @@ shallow_clone: true
 
 environment:
   matrix:
-    - { NODE_VERSION: 6, DIALECT: mssql, COVERAGE: true }
+    - { NODE_VERSION: 8, DIALECT: mssql, COVERAGE: true }
 
 install:
   - ps: Install-Product node $env:NODE_VERSION x64

docs/index.md

@@ -21,7 +21,7 @@
 
 Sequelize is a promise-based Node.js ORM for Postgres, MySQL, MariaDB, SQLite and Microsoft SQL Server. It features solid transaction support, relations, eager and lazy loading, read replication and more.
 
-Sequelize follows [SEMVER](http://semver.org). Supports Node v6 and above to use ES6 features.
+Sequelize follows [SEMVER](http://semver.org). Supports Node v8 and above to use ES2018 features.
 
 **Sequelize v5** was released on March 13, 2019. [Official TypeScript typings are now included](manual/typescript).
 

docs/upgrade-to-v6.md

+# Upgrade to v5
+
+Sequelize v5 is the next major release after v4
+
+## Breaking Changes
+
+### Support for Node 8 and up
+
+Sequelize v6 will only support Node 8 and up