not use Coverage in travis CI; keep it simple

Author: panlanfeng

.travis.yml

@@ -10,5 +10,3 @@ matrix:
   - julia: nightly
 notifications:
     email: false
-after_success:
-    - julia -e 'cd(Pkg.dir("KernelEstimator")); Pkg.add("Coverage"); using Coverage; Coveralls.submit(Coveralls.process_folder())';