Changing min sdk to 25

Change-Id: I0d28069967854357ca755bf25dec19d4979bdecf
diff --git a/build.gradle b/build.gradle
index 4191d47..ab97687 100644
--- a/build.gradle
+++ b/build.gradle
@@ -17,7 +17,7 @@
     buildToolsVersion BUILD_TOOLS_VERSION
 
     defaultConfig {
-        minSdkVersion 21
+        minSdkVersion 25
         targetSdkVersion 28
         versionCode 1
         versionName "1.0"