Update minSdkVersion to 23

Change-Id: I8dc2138bbc00e153542500abbd660bcb5b096f90
diff --git a/build.gradle b/build.gradle
index 641e0bc..5b4f7cd 100644
--- a/build.gradle
+++ b/build.gradle
@@ -6,7 +6,7 @@
 // Android Library configuration
 android {
     defaultConfig {
-        minSdkVersion 21
+        minSdkVersion 23
     }
 
     packagingOptions {