Using 18 as the API level to build libaom with encoder

Author: Javernaut

.travis.yml

@@ -17,4 +17,4 @@ install:
   - curl http://archive.ubuntu.com/ubuntu/pool/universe/n/nasm/nasm_2.14.02-1_amd64.deb --output $HOME/nasm_2.14.02-1_amd64.deb
   - sudo dpkg -i $HOME/nasm_2.14.02-1_amd64.deb
 script:
-  - bash -e ffmpeg-android-maker.sh --enable-libdav1d --enable-libmp3lame --enable-libaom
+  - bash -e ffmpeg-android-maker.sh --enable-libdav1d --enable-libmp3lame --enable-libaom --android-api-level=18