Fix for Travis build stopping on tzdata install prompt

.travis.yml

@@ -26,7 +26,7 @@ install:
   - $SH "wget -q -O - https://apt.mopidy.com/mopidy.gpg | apt-key add -"
   - $SH "wget -q -O /etc/apt/sources.list.d/mopidy.list https://apt.mopidy.com/stretch.list"
   - $SH "apt-get -qq update"
-  - $SH "apt-get install -y build-essential clang clang-tools git autotools-dev autoconf libtool gettext gawk gperf antlr3 libantlr3c-dev libconfuse-dev libunistring-dev libsqlite3-dev libavcodec-dev libavformat-dev libavfilter-dev libswscale-dev libavutil-dev libasound2-dev libmxml-dev libgcrypt20-dev libavahi-client-dev zlib1g-dev libevent-dev libplist-dev libsodium-dev libcurl4-openssl-dev libjson-c-dev libprotobuf-c-dev libpulse-dev libwebsockets-dev libgnutls28-dev libspotify-dev"
+  - $SH "DEBIAN_FRONTEND=noninteractive apt-get install -yq build-essential clang clang-tools git autotools-dev autoconf libtool gettext gawk gperf antlr3 libantlr3c-dev libconfuse-dev libunistring-dev libsqlite3-dev libavcodec-dev libavformat-dev libavfilter-dev libswscale-dev libavutil-dev libasound2-dev libmxml-dev libgcrypt20-dev libavahi-client-dev zlib1g-dev libevent-dev libplist-dev libsodium-dev libcurl4-openssl-dev libjson-c-dev libprotobuf-c-dev libpulse-dev libwebsockets-dev libgnutls28-dev libspotify-dev"
 
 script:
   - $SH "autoreconf -fi"