Fix issue with Jitpack build

Fix a problem when building the Android lib with Jitpack. Log of the issue:

• https://jitpack.io/org/matrix/gitlab/matrix-org/olm/3.2.3/build.log

Hint to fix that:

• https://github.com/AppDevNext/Moka/pull/77/files

Tested OK locally when using this branch on Element Android using:

implementation 'org.matrix.gitlab.matrix-org:olm:bma~fix_jitpack-SNAPSHOT'

Log of the build OK:

• https://jitpack.io/org/matrix/gitlab/matrix-org/olm/bma~fix_jitpack-3.2.3-g995def9-1/build.log

So once this is merged and Olm 3.2.4 released, this should work properly:

implementation 'org.matrix.gitlab.matrix-org:olm:3.2.4'