Follow up to 536823ce55 for the tgs.Dockerfile (#1448)

tgs.Dockerfile

@@ -1,15 +1,11 @@
 FROM alpine AS builder
 
-COPY . /go/src/github.com/42wim/matterbridge
+COPY . /go/src/matterbridge
 RUN apk add \
     go \
     git \
-    gcc \
-    musl-dev \
-  && cd /go/src/github.com/42wim/matterbridge \
-  && export GOPATH=/go \
-  && go get \
-  && go build -x -ldflags "-X main.githash=$(git log --pretty=format:'%h' -n 1)" -o /bin/matterbridge
+  && cd /go/src/matterbridge \
+  && go build -mod vendor -ldflags "-X main.githash=$(git log --pretty=format:'%h' -n 1)" -o /bin/matterbridge
 
 FROM alpine
 RUN apk --no-cache add \