increment version number to 0.21.6

NEWS

+ver 0.21.6 (not yet released)
+
 ver 0.21.5 (2019/02/22)
 * protocol
   - fix deadlock in "albumart" command

android/AndroidManifest.xml

@@ -2,8 +2,8 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
           package="org.musicpd"
           android:installLocation="auto"
-          android:versionCode="27"
-          android:versionName="0.21.5">
+          android:versionCode="28"
+          android:versionName="0.21.6">
 
   <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="26"/>
 

doc/conf.py

@@ -38,7 +38,7 @@ author = 'Max Kellermann'
 # built documents.
 #
 # The short X.Y version.
-version = '0.21.5'
+version = '0.21.6'
 # The full version, including alpha/beta/rc tags.
 release = version
 

meson.build

 project(
   'mpd',
   ['c', 'cpp'],
-  version: '0.21.5',
+  version: '0.21.6',
   meson_version: '>= 0.47.2',
   default_options: [
     'c_std=c99',