Install latest cmake

The build script, build_sparkd.sh, uses the '-S' option, which wasn't
introduced until v3.13

Dockerfile

@@ -2,12 +2,21 @@ FROM ubuntu:bionic
 
 
 RUN apt-get update && \
-DEBIAN_FRONTEND=noninteractive apt-get install -y gnupg wget 
+DEBIAN_FRONTEND=noninteractive apt-get install -y \
+  gnupg \
+  software-properties-common \
+  wget
 
 RUN \
 echo "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-9 main" >> /etc/apt/sources.list && \
 wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key > llvm_key && apt-key add llvm_key
 
+# Add Kitware repo to get latest cmake
+RUN \
+    wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null | apt-key add - && \
+    apt-add-repository 'deb https://apt.kitware.com/ubuntu/ bionic main' && \
+    apt update
+
 RUN \
 apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y \
  libllvm-9-ocaml-dev libllvm9 llvm-9 llvm-9-dev llvm-9-doc llvm-9-examples llvm-9-runtime \
@@ -50,6 +59,7 @@ apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y \
  pkg-config \
  python-pip \
  python3-pip \
+ python3-venv \
  screen \
  silversearcher-ag \
  sudo \