try setting rstudio lock-type to occassional avoid error on shared volumes

rstudio/Dockerfile

@@ -57,7 +57,9 @@ RUN apt-get update \
 	&& chown rstudio:rstudio /home/rstudio \
 	&& addgroup rstudio staff \
   ## Prevent rstudio from deciding to use /usr/bin/R if a user apt-get installs a package
-  &&  echo 'rsession-which-r=/usr/local/bin/R' >> /etc/rstudio/rserver.conf \ 
+  &&  echo 'rsession-which-r=/usr/local/bin/R' >> /etc/rstudio/rserver.conf \
+  ## use more robust file locking to avoid errors when using shared volumes:
+  && echo 'lock-type=advisory' >> /etc/rstudio/file-locks \ 
   ## configure git not to request password each time 
   && git config --system credential.helper 'cache --timeout=3600' \
   && git config --system push.default simple \