Bump version to 1.2.5, update changelog

Author: mat-hek

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 ## 1.2.5 
  * Add tutorials [#1007](https://github.com/membraneframework/membrane_core/pull/1007), plugins [#1012](https://github.com/membraneframework/membrane_core/pull/1012) and demos [#1013](https://github.com/membraneframework/membrane_core/pull/1013) to the docs.
+ * Avoid division by 0 in stalker under weird timer behaviour [#1035](https://github.com/membraneframework/membrane_core/pull/1035)
 
 ## 1.2.4
  * Add `:handle_end_of_stream` and `:handle_start_of_stream` options to debug elements. [#993](https://github.com/membraneframework/membrane_core/pull/993)

mix.exs

@@ -1,7 +1,7 @@
 defmodule Membrane.Mixfile do
   use Mix.Project
 
-  @version "1.2.4"
+  @version "1.2.5"
   @source_ref "v#{@version}"
 
   def project do