update .travis_ci yml

Author: chris-german

.travis.yml

@@ -1,5 +1,4 @@
 language: julia
-sudo: required
 os:
   - linux
   - osx
@@ -8,9 +7,6 @@ julia:
   - 1.0
   - 1.4
   - nightly
-matrix:
-  allow_failures:
-    - julia: nightly
 addons:
     apt_packages:
         - gfortran
@@ -25,13 +21,15 @@ git:
 after_success:
   - julia -e 'using Pkg, MendelPlots; cd(joinpath(dirname(pathof(MendelPlots)), "..")); Pkg.add("Coverage"); using Coverage; Codecov.submit(process_folder()); Coveralls.submit(process_folder())'
 
-
 jobs:
+  allow_failures:
+    - julia: nightly
   include:
     - stage: "Documentation"
       julia: 1.4
-      os: osx
+      os: linux
       script:
         - julia -e 'using Pkg; Pkg.add("Documenter")'
         - julia -e 'using MendelPlots; include(joinpath(dirname(pathof(MendelPlots)), "..", "docs", "make.jl"))'
-      after_script: skip
+      after_script: skip
+      after_success: skip