use /opt/ instead of /etc/ for binary storage

Dockerfile

@@ -2,12 +2,12 @@
 FROM buildpack-deps:buster-curl
 
 LABEL maintainer="ANAGO Ronnel <anagoandy@gmail.com>"
-WORKDIR /etc/vlang
+WORKDIR /opt/vlang
 RUN apt-get -yq update && \
     apt-get install -y --no-install-recommends gcc clang make && \
     rm -rf /var/lib/apt/lists/*
 COPY . .
 RUN make && \
-    ln -s /etc/vlang/v /usr/local/bin/v
+    ln -s /opt/vlang/v /usr/local/bin/v
 
 CMD [ "bash" ]