[gitpod] Update Node.js v10 pinning code

Signed-off-by: Jan Keromnes <jan.keromnes@typefox.io>

.gitpod.dockerfile

@@ -14,8 +14,10 @@ RUN sudo apt-get update \
     && sudo rm -rf /var/lib/apt/lists/*
 
 # Pin Node.js to v10.
+ENV NODE_VERSION="10.19.0"
 RUN bash -c ". .nvm/nvm.sh \
-    && nvm install 10 \
-    && nvm use 10 \
-    && nvm alias default 10 \
+    && nvm install $NODE_VERSION \
+    && nvm use $NODE_VERSION \
+    && nvm alias default $NODE_VERSION \
     && npm install -g yarn"
+ENV PATH=$HOME/.nvm/versions/node/v${NODE_VERSION}/bin:$PATH