update version number at master branch (#1996)

* Update VERSION.txt

* Update .appveyor.yml

* Update DESCRIPTION

.appveyor.yml

@@ -1,4 +1,4 @@
-version: 2.2.3.{build}
+version: 2.2.4.{build}
 
 image: Visual Studio 2015
 platform: x64

R-package/DESCRIPTION

@@ -1,7 +1,7 @@
 Package: lightgbm
 Type: Package
 Title: Light Gradient Boosting Machine
-Version: 2.2.3
+Version: 2.2.4
 Date: 2019-02-05
 Authors@R: c(
 	person("Guolin", "Ke", email = "guolin.ke@microsoft.com", role = c("aut", "cre")),

VERSION.txt

@@ -1 +1 @@
-2.2.3
+2.2.4