Upgrade to Jest 19 (#762)

* Upgrade to Jest 19

* Use exact versions for Jest

tests/flow/node_tests/basic_node_modules/__snapshots__/jsfmt.spec.js.snap

@@ -1,8 +1,10 @@
-exports[`test foo.js 1`] = `
-"var x = require(\'bar.js\');
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`foo.js 1`] = `
+"var x = require('bar.js');
 console.log(x);
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-var x = require(\"bar.js\");
+var x = require(\\"bar.js\\");
 console.log(x);
 "
 `;