docker: update build (#1375)

Dockerfile

@@ -1,10 +1,29 @@
-FROM haskell:8.10.4 AS build-stage
-# if you encounter "version `GLIBC_2.28' not found" error when running
-# chat client executable, build with the following base image instead:
-# FROM haskell:8.10.4-stretch AS build-stage
+FROM ubuntu:focal AS build
+
+# Install curl and simplex-chat-related dependencies
+RUN apt-get update && apt-get install -y curl git build-essential libgmp3-dev zlib1g-dev
+
+# Install ghcup
+RUN a=$(arch); curl https://downloads.haskell.org/~ghcup/$a-linux-ghcup -o /usr/bin/ghcup && \
+    chmod +x /usr/bin/ghcup
+
+# Install ghc
+RUN ghcup install ghc 8.10.7
+# Install cabal
+RUN ghcup install cabal
+# Set both as default
+RUN ghcup set ghc 8.10.7 && \
+    ghcup set cabal
+
 COPY . /project
 WORKDIR /project
-RUN stack install
+
+# Adjust PATH
+ENV PATH="/root/.cabal/bin:/root/.ghcup/bin:$PATH"
+
+# Compile simplex-chat
+RUN cabal update
+RUN cabal install
 
 FROM scratch AS export-stage
-COPY --from=build-stage /root/.local/bin/simplex-chat /
+COPY --from=build /root/.cabal/bin/simplex-chat /