Bump acorn from 5.7.3 to 5.7.4 (facebook#3048)

Summary:
Bumps [acorn](https://github.com/acornjs/acorn) from 5.7.3 to 5.7.4.
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/acornjs/acorn/commit/6370e90067552022710190319cbbbd8c43001957"><code>6370e90</code></a> Mark version 5.7.4</li>
<li><a href="https://github.com/acornjs/acorn/commit/fbc15b1344f6dfb992f67b4bbf1357436247c8a0"><code>fbc15b1</code></a> More rigorously check surrogate pairs in regexp validator</li>
<li>See full diff in <a href="https://github.com/acornjs/acorn/compare/5.7.3...5.7.4">compare view</a></li>
</ul>
</details>
<br />

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</details>
Pull Request resolved: facebook#3048

Reviewed By: jstejada

Differential Revision: D20463740

Pulled By: kassens

fbshipit-source-id: daf7dbff3f2e712f2deb28ee928c9b3437a03d0d

yarn.lock

@@ -994,9 +994,9 @@ acorn-walk@^6.0.1:
   integrity sha512-OtUw6JUTgxA2QoqqmrmQ7F2NYqiBPi/L2jqHyFtllhOUvXYQXf0Z1CYUinIfyT4bTCGmrA7gX9FvHA81uzCoVw==
 
 acorn@^5.5.3:
-  version "5.7.3"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.7.3.tgz#67aa231bf8812974b85235a96771eb6bd07ea279"
-  integrity sha512-T/zvzYRfbVojPWahDsE5evJdHb3oJoQfFbsrKM7w5Zcs++Tr257tia3BmMP8XYVjp1S9RZXQMh7gao96BlqZOw==
+  version "5.7.4"
+  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.7.4.tgz#3e8d8a9947d0599a1796d10225d7432f4a4acf5e"
+  integrity sha512-1D++VG7BhrtvQpNbBzovKNc1FLGGEE/oGe7b9xJm/RFHMBeUaUGpluV9RLjZa47YFdPcDAenEYuq9pQPcMdLJg==
 
 acorn@^6.0.1, acorn@^6.0.2, acorn@^6.0.5:
   version "6.1.1"