[Docker] Add multicore support to "make" and "bundler" (#4544)

* Let make and bundler use multiple cores

* Adds -j option to bundle install instead of bundle config

Dockerfile

@@ -48,7 +48,7 @@ RUN echo "@edge https://nl.alpinelinux.org/alpine/edge/main" >> /etc/apk/reposit
  && rm libiconv.tar.gz \
  && cd /tmp/src/libiconv-$LIBICONV_VERSION \
  && ./configure --prefix=/usr/local \
- && make \
+ && make -j$(getconf _NPROCESSORS_ONLN)\
  && make install \
  && libtool --finish /usr/local/lib \
  && cd /mastodon \
@@ -57,7 +57,7 @@ RUN echo "@edge https://nl.alpinelinux.org/alpine/edge/main" >> /etc/apk/reposit
 COPY Gemfile Gemfile.lock package.json yarn.lock /mastodon/
 
 RUN bundle config build.nokogiri --with-iconv-lib=/usr/local/lib --with-iconv-include=/usr/local/include \
- && bundle install --deployment --without test development \
+ && bundle install -j$(getconf _NPROCESSORS_ONLN) --deployment --without test development \
  && yarn --ignore-optional --pure-lockfile
 
 COPY . /mastodon