fix linting issues

Co-authored-by: Jason Nguyen <jason-nguyen@pluralsight.com>
Co-authored-by: Bret Hubbard <bret-hubbard@pluralsight.com

Author: wes-novack

test/unit.js

@@ -1,3 +1,4 @@
+'use strict'
 const sinon = require('sinon');
 const sinonChai = require('sinon-chai');
 const chai = require('chai');
@@ -96,7 +97,7 @@ describe('node-vault', () => {
           defaults: defaultsStub,
         },
       };
-      vault = index(vaultConfig);
+      const vault = index(vaultConfig);
       vault.endpoint.should.equal('http://localhost:8200');
     });
 
@@ -108,9 +109,9 @@ describe('node-vault', () => {
           defaults: defaultsStub,
         },
       };
-      vault = index(vaultConfig);
+      const vault = index(vaultConfig);
       vault.endpoint.should.equal('http://localhost:8200');
-    })
+    });
   });
 
   describe('client', () => {