Fix build and add Python 3.9

[brbickel]

There are existing TravisCI build errors on the setup and installation of some dependencies. These changes address the build errors. They include:

• Install swig (needed to build M2Crypto dependency)
• Change URL of XORSearch V1.11.3 binary download
• Modify xorsearch path modification to work in other repos (not specifically PUNCH-Cyber's base repo)
• Add Python 3.9 as a build/test target