Parallel compilation

docker/Dockerfile.ArchLinux

@@ -37,7 +37,7 @@ WORKDIR /tmp
 # buid package for qt5-webkit from AUR
 RUN git clone https://aur.archlinux.org/qt5-webkit.git && \
 cd qt5-webkit && \
-makepkg --noconfirm && \
+MAKEFLAGS="-j$(nproc)" makepkg --noconfirm && \
 cd ..
 USER root
 # install the package
@@ -46,7 +46,7 @@ rm -rf /tmp/qt5-webkit
 # build package for wkhtmltopdf from AUR
 RUN git clone https://aur.archlinux.org/wkhtmltopdf.git && \
 cd wkhtmltopdf && \
-makepkg --noconfirm && \
+MAKEFLAGS="-j$(nproc)" makepkg --noconfirm && \
 cd ..
 USER root
 # install the package