Bump min supported elixir version to 1.8 (#184)

* Update consumer docs - remove `spawn` reference in the consumer concurrency mode
* Drop support for `elixir 1.7` - it is old enough
* Test with `OTP22` on travis as well

.travis.yml

@@ -1,12 +1,12 @@
 language: elixir
 elixir:
-  - 1.7
   - 1.8
   - 1.9
   - 1.10
 
 otp_release:
   - 21.0
+  - 22.0
 
 sudo: required
 

lib/consumer.ex

@@ -63,8 +63,8 @@ defmodule GenRMQ.Consumer do
   [recommended](https://www.rabbitmq.com/priority.html#resource-usage).
 
   `concurrency` - defines if `handle_message` callback is called
-  in separate process using [spawn](https://hexdocs.pm/elixir/Process.html#spawn/2)
-  function. By default concurrency is enabled. To disable, set it to `false`
+  in separate process using [supervised task](https://hexdocs.pm/elixir/Task.Supervisor.html).
+  By default concurrency is enabled. To disable, set it to `false`
 
   `terminate_timeout` - defines how long the consumer will wait for in-flight Tasks to
   complete before terminating the process. The value is in milliseconds and the default

mix.exs

@@ -7,7 +7,7 @@ defmodule GenRMQ.Mixfile do
     [
       app: :gen_rmq,
       version: @version,
-      elixir: "~> 1.7",
+      elixir: "~> 1.8",
       start_permanent: Mix.env() == :prod,
       elixirc_paths: elixirc_paths(Mix.env()),
       deps: deps(),