CMake minimum version error

When attempting to install this package, I get an error about the CMake version. (`--skiptests` has no effect on the result)
```
# zeek --version
zeek version 7.0.3
# zkg --version
zkg 3.0.1-33
# zkg install --force corelight/zeek-globload
Running unit tests for "zeek/corelight/zeek-globload"
error: failed to run tests for zeek/corelight/zeek-globload: package build_command failed, see log in /opt/zeek/var/lib/zkg/logs/zeek-globload-build.log
```

```
cat /opt/zeek/var/lib/zkg/logs/zeek-globload-build.log
...
CMake Error at /opt/zeek/share/zeek/cmake/ZeekPlugin.cmake:139 (message):
Plugin requires CMake 3.5 which is less than Zeek's requirement (3.15.0).
Please update cmake_minimum_required VERSION to 3.15 or higher.
Call Stack (most recent call first):
CMakeLists.txt:25 (include)
...
```

Bumping the minimum version to 3.15 here seems to be the solution.
https://github.com/corelight/zeek-globload/blob/master/CMakeLists.txt#L3

Open CMakeLists.txt at the minimum-version setting near line 3 and compare it with the Zeek build error. Update the minimum version as indicated, then rerun `zkg install --force corelight/zeek-globload` to confirm the package build and tests complete without the CMake version error.

Written by the indexing model from the issue text.