Fix the alpine-based Docker image (#1297)

* Fix the alpine-based Docker image

- alpine needs to explicitly install npm as a sep. package
- Use COPY over ADD to copy in the project code,
  see https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#add-or-copy

* Use COPY over ADD in both Dockerfile and Dockerfile.build

Rationale can be found here:
https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#add-or-copy

* Update Dockerfile.slim.build

Dockerfile

@@ -21,7 +21,7 @@ RUN rm $(which buffalo)
 RUN rm -rf $BP
 RUN mkdir -p $BP
 WORKDIR $BP
-ADD . .
+COPY . .
 
 RUN go get github.com/gobuffalo/buffalo-pop
 RUN make deps

Dockerfile.build

@@ -37,10 +37,10 @@ RUN npm install -g --no-progress yarn \
 
 RUN rm -rfv $BP && mkdir -p $BP
 WORKDIR $BP
-
-ADD . .
+COPY . .
 RUN make deps && make install
 
+
 # cache yarn packages to an offline mirror so they're faster to load. hopefully.
 RUN grep -v '{{' ./generators/assets/webpack/templates/package.json.tmpl > package.json \
 && yarn install --no-progress

Dockerfile.slim.build

@@ -2,7 +2,7 @@ FROM golang:alpine
 EXPOSE 3000
 ENV BP=$GOPATH/src/github.com/gobuffalo/buffalo
 RUN apk add --no-cache --upgrade apk-tools \
-&& apk add --no-cache bash curl openssl git build-base yarn nodejs postgresql libpq postgresql-contrib sqlite sqlite-dev mysql-client vim
+&& apk add --no-cache bash curl openssl git build-base nodejs npm postgresql libpq postgresql-contrib sqlite sqlite-dev mysql-client vim
 
 RUN go version && go get -v -u github.com/markbates/deplist/deplist
 
@@ -24,16 +24,16 @@ RUN go get -u github.com/golang/dep/cmd/dep \
 && go get -u github.com/alecthomas/gometalinter \
 && gometalinter --install
 
-RUN npm install -g --no-progress yarn \
+RUN npm i -g --no-progress yarn \
 && yarn config set yarn-offline-mirror /npm-packages-offline-cache \
 && yarn config set yarn-offline-mirror-pruning true
 
 
 RUN rm -rfv $BP && mkdir -p $BP
 WORKDIR $BP
 
-ADD . .
-RUN go get -tags "sqlite" -v -t github.com/gobuffalo/buffalo/... && make install
+COPY . .
+RUN make deps && make install
 
 # cache yarn packages to an offline mirror so they're faster to load. hopefully.
 RUN grep -v '{{' ./generators/assets/webpack/templates/package.json.tmpl > package.json \