Test fails for Node.js >= 12, and sinon=8.1.1

[nileshpatra]

Test fails with the following error:

/home/nilesh/ups/node-sshpk/test/dhe_compat.js:26
	sandbox = sinon.sandbox.create();
	                        ^

TypeError: Cannot read property 'create' of undefined
    at Test.<anonymous> (/home/nilesh/ups/node-sshpk/test/dhe_compat.js:26:26)
    at Test.bound [as _cb] (/home/nilesh/ups/node-sshpk/node_modules/tape/lib/test.js:62:32)
    at Test.run (/home/nilesh/ups/node-sshpk/node_modules/tape/lib/test.js:75:10)
    at Test.bound [as run] (/home/nilesh/ups/node-sshpk/node_modules/tape/lib/test.js:62:32)
    at Immediate.next (/home/nilesh/ups/node-sshpk/node_modules/tape/lib/results.js:66:15)
    at runCallback (timers.js:705:18)
    at tryOnImmediate (timers.js:676:5)
    at processImmediate (timers.js:658:5)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! sshpk@1.16.1 test: `tape test/*.js`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the sshpk@1.16.1 test script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/nilesh/.npm/_logs/2020-01-28T18_42_59_881Z-debug.log