composer.json: use explicit dependency versions (#1180)
composer.json: use explicit dependency versions (#1180)

This ensures that dev environments and production environments are
using the same dependency versions. It also ensures that dependabot
keeps us properly updated on any new release.

* abraham/twitteroauth: ^3.1 -> 3.2.0
* google/recaptcha: ^1.1 -> 1.2.4
smrealms/smr,hemberger/smr,smrealms/smr,hemberger/smr,hemberger/smr,smrealms/smr,hemberger/smr