fix: update dockerfile for gopls blog

content/blog/2019/2019-11-05-docker-gopls.md

 
 ```Dockerfile
 FROM ubuntu:xenial AS builder
-RUN apt-get update
-# Install system dependencies that we might need
-RUN apt-get install -y gcc g++
+RUN apt-get update && \
+    apt-get install -y gcc g++ libssl-dev cmake wget libpcre3 libpcre3-dev git
 
-# Install Depencies like Go and Swig in our container.
 WORKDIR /tmp
-# Install Go
-RUN wget https://dl.google.com/go/go1.12.9.linux-amd64.tar.gz
-RUN tar -C /usr/local -xzf go1.12.9.linux-amd64.tar.gz
-# Install Swig
-RUN wget http://prdownloads.sourceforge.net/swig/swig-4.0.1.tar.gz
-RUN tar -zxvf swig-4.0.1.tar.gz
-RUN cd /tmp/swig-4.0.1 && ./configure && make && make install
-
-# Create user
-RUN useradd -m -r -u 1000 myuser
-RUN groupmod -g 1000 myuser
-
-# Replicate/fake the host system tree
-RUN mkdir -p /home/myuser/code/go/myhostdir/myproject
-RUN chown -R myuser:myuser /home/myuser/code/go/myhostdir/myproject
+
+# Install Go.
+RUN wget https://dl.google.com/go/go1.12.9.linux-amd64.tar.gz && \
+    tar -C /usr/local -xzf go1.12.9.linux-amd64.tar.gz
+
+# Install Swig.
+RUN wget http://prdownloads.sourceforge.net/swig/swig-4.0.1.tar.gz && \
+    tar -zxvf swig-4.0.1.tar.gz && \
+    cd /tmp/swig-4.0.1 && ./configure && make && make install 
+
+ARG MY_USER_ID
+ENV MY_USER_ID ${MY_USER_ID}
+
+ARG MY_PWD
+ENV MY_PWD ${MY_PWD}
+
+RUN mkdir -p $MY_PWD
+
+RUN useradd -r -m -u $MY_USER_ID myuser
+RUN groupmod -g $MY_USER_ID myuser
 USER myuser
 
-WORKDIR /home/myuser/code/go/myhostdir/myproject
+ENV PATH="/usr/local/go/bin:${MY_PWD}/go/bin:${PATH}"
+RUN GOPROXY=https://proxy.golang.org GO111MODULE=on go get golang.org/x/tools/[email protected]
+WORKDIR $MY_PWD
 
-RUN GO111MODULE=on go get golang.org/x/tools/gopls@latest
-CMD gopls -listen=":7050"
+CMD /home/myuser/go/bin/gopls -listen=":7050"
 ```
 
 Firstly, we install all the dependencies and then create
 Finally, we install gopls in the container and then start it in the container
 with the `-listen=":7050"` flag.
 
+We will now build the image.
+
+```bash
+mkdir -p go
+
+docker build \
+--build-arg MY_PWD=${PWD} \
+--build-arg=MY_USER_ID=${MY_USER_ID} \
+-t myapp:latest .
+```
+
+Note, we also create a directory called `go` which will be the mock GOPATH 
+inside the container.
 
 Now we can expose this port to our host machine.
 
 ```bash
-docker run -d --name "myproject" -u `id -u` -p 7050:7050 \
-    -v /home/myuser/code/go/myhostdir/myproject:/home/myuser/code/go/myhostdir/ \
-    myproject myproject:latest
+docker run -d --name "myapp" \
+-u `id -u ${USER}` \
+-e "GOPATH=${PWD}/go" \
+-p 7050:7050 \
+-v ${PWD}:${PWD} myapp:latest
 ```
 
 Notice, that we also mount the host source in the container with the same path,
 gopls -remote "localhost:7050"
 ```
 
+For VSCode, you can add the following to your `settings.json`
+
+```json
+{
+    "go.languageServerFlags": [
+        "-remote=localhost:7050",
+        "-v"
+    ],
+    "go.useLanguageServer": true,
+    "go.gopath": "go"
+}
+```
+
 After adding this flag, you will now be able to edit your source with all the
-added benefits that come with a language server. 
+added benefits that come with a language server like autocompletion and 
+autoformatting.
 
 Since this is an experimental feature, it might break (a lot). Do let me know 
 in the comments if this was helpful for you.