Increment release number to 3.1

Author: lvaccaro

app/build.gradle

@@ -9,8 +9,8 @@ android {
         applicationId "com.lvaccaro.lamp"
         minSdkVersion 19
         targetSdkVersion 28
-        versionCode 3
-        versionName "3"
+        versionCode 31
+        versionName "3.1"
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
         vectorDrawables.useSupportLibrary = true
     }