Make keytar a required dependency

package.json

@@ -94,6 +94,7 @@
     "is": "^3.1.0",
     "istanbul": "^0.3.17",
     "jsdom-no-contextify": "^3.1.0",
+    "keytar": "^4.0.3",
     "lazy.js": "^0.4.2",
     "mime": "1.2.11",
     "minimatch": "^2.0.10",
@@ -125,7 +126,6 @@
     "url": "https://github.com/Microsoft/vscode/issues"
   },
   "optionalDependencies": {
-    "keytar": "^4.0.3",
     "windows-foreground-love": "0.1.0",
     "windows-mutex": "^0.2.0",
     "fsevents": "0.3.8"