v2.3.0 realese (#2138)

* Update DESCRIPTION

* bump minor version

.appveyor.yml

@@ -1,4 +1,4 @@
-version: 2.2.4.{build}
+version: 2.3.0.{build}
 
 image: Visual Studio 2015
 platform: x64

R-package/DESCRIPTION

@@ -1,8 +1,8 @@
 Package: lightgbm
 Type: Package
 Title: Light Gradient Boosting Machine
-Version: 2.2.4
-Date: 2019-02-05
+Version: 2.3.0
+Date: 2019-04-30
 Authors@R: c(
 	person("Guolin", "Ke", email = "guolin.ke@microsoft.com", role = c("aut", "cre")),
 	person("Damien", "Soukhavong", email = "damien.soukhavong@skema.edu", role = c("ctb")),

VERSION.txt

@@ -1 +1 @@
-2.2.4
+2.3.0