chore: remove TS declaration maps from git [skip ci] (#194)

We can remove this after projen/projen#1896 is addressed upstream.

---

_By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license_

Author: Eugene Cheung

.gitignore

@@ -108,6 +108,9 @@ project.eslint.addRules({
 project.addPackageIgnore("*.ts");
 project.addPackageIgnore("!*.d.ts");
 
+// TODO: remove this once projen ignores these: https://github.com/projen/projen/issues/1896
+project.gitignore.exclude("*.d.ts.map");
+
 project.release.addJobs({
   notify_slack: {
     name: "Send Slack notification",