fixed typo ubus-lime-groundrouting in lime-app's Makefile

[ilario]

That typo was introduced in January 2019 with this commit 8fe8d05 part of #453

It causes this warning and error messages when building LibreMesh using the Buildroot method:

WARNING: Makefile 'package/feeds/libremesh/lime-app/Makefile' has a dependency on 'ubus-lime-grondrouting', which does not exist
 * pkg_hash_check_unresolved: cannot find dependency ubus-lime-grondrouting for lime-app

[ilario]

This error got revealed when testing #1139.

Using this fix, I also got rid of these other errors:

 * pkg_hash_fetch_best_installation_candidate: Packages for lime-app found, but incompatible with the architectures configured
 * opkg_install_cmd: Cannot install package lime-app.

Before the adoption of libremesh.mk in #1139 (see also #766) this is not failing as the same typo is present also in the Makefile (since 1b2d501). After #1139 the package name is taken from the directory name, where the typo is not present.

[a-gave]

Thanks! I seem to have encountered this testing 1139 but skipped because building without lime-app.