build: force bump to release types

[alecjacobs5401]

The 3.0.0 release neglected to include the dist/index.d.ts file in the package, which caused downstream consumers to experience issues with TypeScript type checking. This PR bumps the version to 3.0.1 and includes the missing file in the package.

lerna success published @segment/backstage-plugin-proxy-sigv4-backend 0.3.1
lerna notice
lerna notice 📦  @segment/[email protected]
lerna notice === Tarball Contents ===
lerna notice 11.3kB LICENSE
lerna notice 7.5kB  dist/index.cjs.js
lerna notice 1.7kB  package.json
lerna notice 14.5kB dist/index.cjs.js.map
lerna notice 6.3kB  README.md
lerna notice 1.0kB  config.d.ts
lerna notice 535B   dist/index.d.ts
lerna notice === Tarball Details ===
lerna notice name:          @segment/backstage-plugin-proxy-sigv4-backend
lerna notice version:       0.3.1
lerna notice filename:      segment-backstage-plugin-proxy-sigv4-backend-0.3.1.tgz
lerna notice package size:  13.6 kB
lerna notice unpacked size: 42.8 kB
lerna notice shasum:        8bbc139c85ccfa42086ff9e3bef24a3890464a7b
lerna notice integrity:     sha512-3rDSVic3kcxx7[...]/PmRPPs6ooF0A==
lerna notice total files:   7
lerna notice
Successfully published:
 - @segment/[email protected]

Apparently running yarn build from the root of the repo decided to remove dist/index.d.ts from the package for some reason. We should dig into that since it is another trap waiting to happen.