Updated Dockerfile (#575)

* - added missing dependencies

* - updated protoc version

Docker/Dockerfile

@@ -1,10 +1,13 @@
 FROM swift:latest
 MAINTAINER Tim Burks <timburks@google.com>
 
-ENV PROTOC_VERSION=3.5.1
+ENV PROTOC_VERSION=3.9.1
 
 # Install a few needed packages that aren't in swiftdocker/swift
 RUN apt-get -q update \
+    && apt-get install curl \
+    && apt-get install libz-dev \
+    && apt-get install libssl-dev \
     && apt-get -q install -y unzip libnghttp2-dev \
     && rm -r /var/lib/apt/lists/*