Changes hierfstat to install from Github instead of CRAN

See NESCent/popgenInfo#78 for background discussion. In a nutshell, the function
genind2hierfstat() was removed in recent CRAN release from adegenet, but the version
of hierfstat that now includes it isn't yet updated in CRAN. Once it is, this commit
should be revertible.

Rpopgen/Dockerfile

@@ -9,7 +9,6 @@ RUN rm -rf /tmp/*.rds \
 &&  install2.r --error \
     ape \
     adegenet \
-    hierfstat \
     pegas \
     coalescentMCMC \
     mmod \
@@ -23,8 +22,10 @@ RUN rm -rf /tmp/*.rds \
 RUN Rscript -e 'source("http://bioconductor.org/biocLite.R"); biocLite("qvalue")'
 
 ## Install population genetics packages from Github
+## (hierfstat included here temporarily until new release is on CRAN)
 RUN installGithub.r \
     whitlock/OutFLANK \
+    jgx65/hierfstat \
 && rm -rf /tmp/downloaded_packages/ /tmp/*.rds
 
 ## Install other useful packages from CRAN