Try to get Travais to install dependencies

Author: Alexandre Génin

.travis.yml

@@ -16,7 +16,7 @@ script:
   # Test first the fitting results against pli code
   - R -e "update.packages(ask = FALSE)"
   - R -e "install.packages(c('testthat', 'roxygen2', 'devtools'))"
-  - R -e "devtools::install_deps(dependencies = TRUE)"
+  - R -e "devtools::install_deps(upgrade = 'always', dependencies = TRUE, repos = 'https://cloud.r-project.org')"
   - R -e "EXTENDED_TESTS <- TRUE; devtools::test(filter = 'psdfit')"
   - R -e "EXTENDED_TESTS <- TRUE; devtools::test(filter = 'xmin')"
   - R -e "EXTENDED_TESTS <- TRUE; devtools::test(filter = 'flowlength')"