Use sinon as peer dependency

[laleksiunas]

Currently, sinon is added as a dependency in the package.json. Such package managing causes issues due to two sinon instances running in an end-user project (sinon instance in ts-sinon library and sinon itself in the end-user projects). For example, stubbing class methods using ts-sinon stubConstructor and later on using withArgs(sinon.match(someObject)) function from sinon package does not work correctly due to sinon instances conflicts - methods are not called when they should be. The issue gets fixed when I move this library's code directly to my project and use my sinon instance.
So proposed solution would be to move sinon and its dependencies to peer dependencies list.