Simplify coverage upload in .travis.yml (#2009)

.travis.yml

@@ -1,4 +1,6 @@
 language: julia
+codecov: true
+coveralls: true
 os:
     - linux
 #   - osx # Disable to speed up CI. JuMP has no binary dependency so the result
@@ -18,8 +20,6 @@ addons:
         - gfortran
         - liblapack-dev
         - libblas-dev
-after_success:
-    - julia -e 'using Pkg; Pkg.add("Coverage"); cd(Pkg.dir("JuMP")); using Coverage; Coveralls.submit(process_folder()); Codecov.submit(process_folder())'
 jobs:
   include:
     - stage: "Documentation"