Refactoring install commands into install phase

[keheliya]

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Having install commands in other phases violates the semantics of the .travis.yml configuration. So we have refactored them into the install phase.

If the install phase is not defined in the .travis.yml, Travis CI runs npm install for Node.js projects by default, as explained in the Travis CI docs here. To preserve that original behaviour after refactoring, we have added the npm install command as well.

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Note: This pull request was generated by an automated tool developed by The Software REBELs (a.k.a., the Software Repository Excavation and Build Engineering Labs) of McGill University, Canada. It is part of a research project by Keheliya Gallaba under the supervision of Dr.Shane McIntosh. If you have any questions or feedback about this tool, please feel free to contact the author ([email protected]).