Bump version to v1.2.0-rc0 (#940)

Author: FelonEkonom

CHANGELOG.md

@@ -1,6 +1,6 @@
 # Changelog
 
-## 1.2.0
+## 1.2.0-rc0
  * Add `:max_instances` option for dynamic pads. [#876](https://github.com/membraneframework/membrane_core/pull/876)
  * Implement `Membrane.Connector`. [#904](https://github.com/membraneframework/membrane_core/pull/904)
  * Implememnt diamonds detection. [#909](https://github.com/membraneframework/membrane_core/pull/909)

README.md

@@ -92,6 +92,10 @@ The API for creating pipelines (and custom elements too) is provided by [membran
 ```elixir
 {:membrane_core, "~> 1.1"}
 ```
+or to get the newest release candidate
+```elixir 
+{:membrane_core, "1.2.0-rc0"}
+```
 
 **Standalone libraries**
 

mix.exs

@@ -1,7 +1,7 @@
 defmodule Membrane.Mixfile do
   use Mix.Project
 
-  @version "1.1.2"
+  @version "1.2.0-rc0"
   @source_ref "v#{@version}"
 
   def project do