fix install hhvm package cannot be authenticated

Author: bestlong

hhvm/Dockerfile

@@ -5,7 +5,8 @@ MAINTAINER Mahmoud Zalt <mahmoud@zalt.me>
 RUN apt-key adv --recv-keys --keyserver hkp://keyserver.ubuntu.com:80 0x5a16e7281be7a449
 
 RUN apt-get update -y \
-    && apt-get install -y software-properties-common \
+    && apt-get install -y software-properties-common wget \
+    && wget -O - http://dl.hhvm.com/conf/hhvm.gpg.key | sudo apt-key add - \
     && add-apt-repository "deb http://dl.hhvm.com/ubuntu $(lsb_release -sc) main" \
     && apt-get update -y \
     && apt-get install -y hhvm \