[release] prepare for 1.2.5

# Conflicts:
#	History.md
#	pom.xml
#	src/main/ruby/jruby/rack/version.rb

Author: kares

History.md

@@ -19,7 +19,7 @@
 - Change context listener to throw, in case of an exception during initialization, by default
 - Change rails context listener to assume a thread-safe application by default
 
-## 1.2.5 (UNRELEASED)
+## 1.2.5
 
 - Fix use of jruby-rack under Java 8 (#324)
 - Fix deprecated usages of JRuby runtime