Add ccapi_cpp deps to docker

* Add rapidjson-dev
* Add Kitware repo to get latest cmake (the ccapi_cpp lib relies on
  'add_compile_definitions', which was introduced in cmake 3.12)

Dockerfile

@@ -10,6 +10,13 @@ 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.  The ccapi lib relies on
+# 'add_compile_definitions', which was introduced in cmake 3.12.
+RUN \
+    wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null | sudo apt-key add - && \
+    apt-add-repository 'deb https://apt.kitware.com/ubuntu/ bionic main' && \
+    apt update
+
 # add the latest node repository to apt sources (npm in the standard bionic apt
 # repostitory depends on libssl1.0-dev, but emumba depends on libssl-dev, so a
 # the latest npm must be installed to avoid this dependency conflict
@@ -60,6 +67,7 @@ RUN \
     python-pip \
     python3-pip \
     python3-venv \
+    rapidjson-dev \
     screen \
     silversearcher-ag \
     sudo \
@@ -189,8 +197,7 @@ RUN \
     && sudo apt-get update \
     && sudo apt-get install apt-transport-https -y \
     && sudo apt-get update \
-    && sudo apt-get install dotnet-sdk-2.1 -y \
-    && sudo apt-get install dotnet-sdk-3.1 -y
+    && sudo apt-get install dotnet-sdk-6.0 -y
 
 # Enable detection of running in a container
 ENV DOTNET_RUNNING_IN_CONTAINER=true \