Drop official support for MRI 2.2

Just because we can't test this properly anymore, it does not mean
it doesn't work with MRI 2.2 anymore...

Author: dmke

.travis.yml

@@ -2,10 +2,9 @@ sudo: required
 dist: trusty
 language: ruby
 before_install:
-  - bin/travis.sh
+  - gem update --system --no-doc
   - bin/provision.sh
 rvm:
-  - "2.2"
   - "2.3"
   - "2.4"
   - "2.5"

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 For the full commit log, [see here](https://github.com/influxdata/influxdb-ruby/commits/master).
 
+## unreleased
+
+- Drop support for Ruby 2.2, since Bundler dropped it and we want to use
+  Bundler in the development cycle as well.
+
 ## v0.6.4, releases 2018-12-02
 
 - Fix newly introduced `InfluxDB.now(precision)` for precisions larger

README.md

@@ -39,8 +39,10 @@ Maintained by [@toddboom](https://github.com/toddboom) and [@dmke](https://githu
 
 ## Ruby support
 
-Since v0.4.0, this gem requires Ruby >= 2.2.0. Support for MRI < 2.2 is
-still available in the v0.3.x series, see [stable-03 branch](https://github.com/influxdata/influxdb-ruby/tree/stable-03)
+Since v0.7.0, this gem requires Ruby >= 2.3.0. MRI 2.2 *should* still work,
+however we are unable to test this properly, since our toolchain (Bundler)
+has dropped support for it. Support for MRI < 2.2 is still available in the
+v0.3.x series, see [stable-03 branch](https://github.com/influxdata/influxdb-ruby/tree/stable-03)
 for documentation.
 
 ## Installation