travis build fail: magic

[bradfordcondon]

Configuration failed because Magick++ was not found. Try installing:
 - deb: 'libmagick++-dev' (Debian, Ubuntu)
 - rpm: 'ImageMagick-c++-devel' (Fedora, CentOS, RHEL)
 - csw: 'imagemagick_dev' (Solaris)
On MacOS it is recommended to use install ImageMagick-6 from homebrew
with extra support for fontconfig and rsvg rendering:
   brew reinstall imagemagick@6 --with-fontconfig --with-librsvg
For older Ubuntu versions Trusty (14.04) and Xenial (16.04) use our PPA:
   sudo add-apt-repository -y ppa:opencpu/imagemagick
   sudo apt-get update
   sudo apt-get install -y libmagick++-dev
If Magick++ is already installed, check that 'pkg-config' is in your
PATH and PKG_CONFIG_PATH contains a Magick++.pc file. If pkg-config
is unavailable you can set INCLUDE_DIR and LIB_DIR manually via:
R CMD INSTALL --configure-vars='INCLUDE_DIR=... LIB_DIR=...'
--------------------------------------------------------------------
ERROR: configuration failed for package ‘magick’
* removing ‘/home/travis/R/Library/magick’
Error in i.p(...) : 
  (converted from warning) installation of package ‘magick’ had non-zero exit status
Calls: <Anonymous> ... with_rprofile_user -> with_envvar -> force -> force -> i.p
Execution halted
The command "Rscript -e 'deps <- devtools::dev_package_deps(dependencies = NA);devtools::install_deps(dependencies = TRUE);if (!all(deps$package %in% installed.packages())) { message("missing: ", paste(setdiff(deps$package, installed.packages()), collapse=", ")); q(status = 1, save = "no")}'" failed and exited with 1 during .

perhaps related to #15 in that if installation is done properly in the vignette we might resolve it?

[bradfordcondon]

this looks resolved.
Now we just have our warnigns treated as errors so its failing. Maybe we can turn off that strictness so it will pass.

Found warnings, treating as errors (as requested).