Bump acorn from 5.4.0 to 5.7.4 in /examples/web

Bumps [acorn](https://github.com/acornjs/acorn) from 5.4.0 to 5.7.4.
- [Release notes](https://github.com/acornjs/acorn/releases)
- [Commits](acornjs/acorn@5.4.0...5.7.4)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

examples/web/yarn.lock

@@ -1226,14 +1226,10 @@ acorn-walk@^6.0.1:
   resolved "https://registry.yarnpkg.com/acorn-walk/-/acorn-walk-6.1.1.tgz#d363b66f5fac5f018ff9c3a1e7b6f8e310cc3913"
   integrity sha512-OtUw6JUTgxA2QoqqmrmQ7F2NYqiBPi/L2jqHyFtllhOUvXYQXf0Z1CYUinIfyT4bTCGmrA7gX9FvHA81uzCoVw==
 
-acorn@^5.0.0:
-  version "5.4.0"
-  resolved "https://registry.npmjs.org/acorn/-/acorn-5.4.0.tgz#51c581c9d4b1943dda59a3e73bcf02661ac727ea"
-
-acorn@^5.5.3, acorn@^5.6.2:
-  version "5.7.3"
-  resolved "https://registry.yarnpkg.com/acorn/-/acorn-5.7.3.tgz#67aa231bf8812974b85235a96771eb6bd07ea279"
-  integrity sha512-T/zvzYRfbVojPWahDsE5evJdHb3oJoQfFbsrKM7w5Zcs++Tr257tia3BmMP8XYVjp1S9RZXQMh7gao96BlqZOw==
+acorn@^5.0.0, acorn@^5.5.3, acorn@^5.6.2:
+  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@^6.0.7:
   version "6.1.1"