doc+build: Prepare release 0.2.1

This commit also fixes build issue on Travis-CI

Change-Id: Ic48ec8ca5b196cd02215622284656aca78582aa0
diff --git a/app/build.gradle b/app/build.gradle
index b37327a..374c9d5 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -10,8 +10,8 @@
         applicationId "net.named_data.nfd"
         minSdkVersion 15
         targetSdkVersion 19
-        versionCode 3005
-        versionName "0.3.4"
+        versionCode 4001
+        versionName "0.2.1 (NFD 0.4.0-3-g4100646)"
     }
     compileOptions {
         sourceCompatibility JavaVersion.VERSION_1_7