Add dbus to list of Debian build deps

README.md

@@ -41,7 +41,7 @@ sudo apt-get install git curl freeglut3-dev autoconf \
     libfreetype6-dev libgl1-mesa-dri libglib2.0-dev xorg-dev \
     gperf g++ build-essential cmake virtualenv python-pip \
     libssl-dev libbz2-dev libosmesa6-dev libxmu6 libxmu-dev \
-    libglu1-mesa-dev libgles2-mesa-dev libegl1-mesa-dev
+    libglu1-mesa-dev libgles2-mesa-dev libegl1-mesa-dev libdbus-1-dev
 ```
 If you are on **Ubuntu 14.04** and encountered errors on installing these dependencies involving `libcheese`, see [#6158](https://github.com/servo/servo/issues/6158) for a workaround.