Clean up: Removes trailing whitespace

docker/Dockerfile

@@ -6,7 +6,7 @@ RUN rm /etc/pacman.d/mirrorlist
 RUN echo 'Server = http://ftp.jaist.ac.jp/pub/Linux/ArchLinux/$repo/os/$arch'    >> /etc/pacman.d/mirrorlist
 RUN echo 'Server = http://ftp.tsukuba.wide.ad.jp/Linux/archlinux/$repo/os/$arch' >> /etc/pacman.d/mirrorlist
 
-RUN rm /etc/localtime 
+RUN rm /etc/localtime
 RUN ln -s /usr/share/zoneinfo/Asia/Tokyo /etc/localtime
 
 RUN pacman -Sy --noconfirm