Fix AppVeyor missing dependency (openssl)

[geneorama]

From issue #158

The TravisCI build for release R is working. The AppVeyor build is failing while installing R packages, specifically openssl. It looks like it is building openssl from source and is hitting a bug or configuration issue, because it cannot find gcc to compile the package.

I believe that this commit would pass if not for this issue, and the CRAN builds do not show the openssl error.

One of the release R builds fails on an error that looks to be unrelated to our code, and I noticed some other packages on CRAN are getting the same failure.

I'm going to move forward in the interest of time.

[geneorama]

Based on the discussion here it looks like we can fix this by installing libssl-dev.

With travis-ci we would just do this, but not sure for AppVeyor.

before_install:
  - sudo apt-get update
  - sudo apt-get install -y libssl-dev

[tomschenkjr]

I started branch issue160. Generally, you can insert the following to invoke Appveyor to run shell-compatible commands:

install:
  - sh sudo apt-get install -y libssl-dev

But the build for issue160 failed with an extensive error message related to the purr package. Likewise, @nicklucius also failed with the same message. This indicates that the error may not be related to libssl-dev.

Before diving-in deeper, is libssl-dev still the issue with Appveyor, or did this conversation shift?

[nicklucius]

I think the problem is on any package that is compiled from source. So it was openssl the other day, and today it's purrr. Here is the pertinent message:

There is a binary version available but the source version is later:
       binary source needs_compilation
purrr  0.2.5  0.3.0              TRUE

When installing from source, the Appveyor machine is looking for gcc in c:/Rtools/mingw_32/bin/gcc, but it cannot find it.

/bin/sh: c:/Rtools/mingw_32/bin/gcc: No such file or directory

So it's just looking in the wrong place for gcc, I think. From the log it looks like it's installed in:

C:\Rtools\mingw_64\bin