Upgrade flow to 63.1 (firefox-devtools#5075)

Author: AnshulMalik

.flowconfig

@@ -12,5 +12,4 @@
 ./src/global-types.js
 
 [options]
-unsafe.enable_getters_and_setters=true
 suppress_comment=\\(.\\|\n\\)*\\$FlowIgnore

package.json

@@ -128,7 +128,7 @@
     "eslint-plugin-prettier": "^2.3.1",
     "eslint-plugin-react": "^7.2.1",
     "expect.js": "^0.3.1",
-    "flow-bin": "0.61.0",
+    "flow-bin": "0.63.1",
     "glob": "^7.0.3",
     "husky": "^0.14.2",
     "jest": "^20.0.4",