Fix travis build script

[riyadparvez]

The Travis Build status is available at https://travis-ci.org/riyadparvez/data-structures-csharp

[mohanprasathsj]

Hi Riyad,
The project build is not successful. The solution do have lot of errors. Shall I make few changes in the files and send you a PR as a whole. Please note that we need to change a lot of files.

Other solution would be Unload all the projects and load only the projects which are building successfully. There will be only change in the solution file.

My recommendation would be option 2.

[riyadparvez]

NP. I did a lousy job when I've added some classes.
Thanks for the PR.