Contacts: Up minimum SDK to 26

* Adaptive Icon won't work on anything sub-26.

Change-Id: Ie1bda5d4b382d568fd20a4a3dea3aacb7631cc9e
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 24cc3ec..e820f4c 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -20,7 +20,7 @@
           android:versionName="1.7.31">
 
     <uses-sdk
-        android:minSdkVersion="21"
+        android:minSdkVersion="26"
         android:targetSdkVersion="28"/>
 
     <original-package android:name="com.android.contacts"/>