[meson] find versionManager.sh relative to the current meson.build file

emper/include/meson.build

@@ -3,6 +3,6 @@ emper_include = include_directories('.')
 emper_version_h = custom_target(
   'emper-version.h',
   output: 'emper-version.h',
-  command: ['@SOURCE_DIR@/scripts/versionManager.sh', 'check', meson.project_version()]
+  command: ['@CURRENT_SOURCE_DIR@/../../scripts/versionManager.sh', 'check', meson.project_version()]
 )
 emper_generated_files += emper_version_h