fix(package.json): use the latest version of Mongoose

we use latest version of Mongoose to suppress the warning message:
npm WARN unmet dependency /home/user/version-control/git/mykabam/kabam/node_modules/kabam-plugin-migrate/node_modules/mongoose-migrate requires mongoose@'latest' but will load
npm WARN unmet dependency /home/user/version-control/git/mykabam/kabam/node_modules/kabam-plugin-migrate/node_modules/mongoose,
npm WARN unmet dependency which is version 3.6.20