Bump expiry date to 31 December 2018.

briar-android/src/main/java/org/briarproject/briar/android/BriarApplication.java

@@ -6,8 +6,8 @@ package org.briarproject.briar.android;
  */
 public interface BriarApplication {
 
-	// This build expires on 31 December 2017
-	long EXPIRY_DATE = 1514761200 * 1000L;
+	// This build expires on 31 December 2018
+	long EXPIRY_DATE = 1546214400 * 1000L;
 
 	AndroidComponent getApplicationComponent();