Update .travis.yml for julia 1.0: Add using Pkg (#72)

Add `using Pkg` before `Pkg.add()` statements in `after_success`

Author: NHDaly

.travis.yml

@@ -17,5 +17,5 @@ notifications:
   email: false
 
 after_success:
-  - julia -e 'Pkg.add("Coverage"); cd(Pkg.dir("PkgBenchmark")); using Coverage; Coveralls.submit(Coveralls.process_folder())'
-  - julia -e 'Pkg.add("Documenter"); cd(Pkg.dir("PkgBenchmark")); include(joinpath("docs", "make.jl"))'
+  - julia -e 'using Pkg; Pkg.add("Coverage"); using Coverage; Coveralls.submit(Coveralls.process_folder())'
+  - julia -e 'using Pkg; Pkg.add("Documenter"); include(joinpath("docs", "make.jl"))'