[pkg:js] Update version constraint
[pkg:js] Update version constraint

Matches the version of the final CL in the stack of changes for
@JSExport: https://github.com/dart-lang/sdk/commit/81ba8a2583d4edca4898531433942f5fd0ea5292

Change-Id: I3a86d542adcaa030c6056c8afec6dd8b2208f4e6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/265963
Commit-Queue: Srujan Gaddam <4175f2f2dd3cde6c8ffb10fc9674dc09abf813fe@google.com>
Reviewed-by: Kevin Moore <1d6e7d10d051cf619c5282da3c28fd8d3e0a65a4@google.com>
Auto-Submit: Srujan Gaddam <4175f2f2dd3cde6c8ffb10fc9674dc09abf813fe@google.com>
Commit-Queue: Kevin Moore <1d6e7d10d051cf619c5282da3c28fd8d3e0a65a4@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk