CMake modules must be in cmake subdir.

--- a/CMakeLists.txt	2017-05-19 17:01:08.000000000 +0200
+++ b/CMakeLists.txt	2019-11-26 23:50:40.660462479 +0100
@@ -368,10 +368,10 @@
 
 # export targets:
 INSTALL(EXPORT vigra-targets
-        DESTINATION lib${LIB_SUFFIX}/vigra)
+        DESTINATION lib${LIB_SUFFIX}/cmake/vigra)
 INSTALL(FILES ${PROJECT_BINARY_DIR}/lib/vigra/CMake/VigraConfig.cmake
             ${PROJECT_BINARY_DIR}/lib/vigra/CMake/VigraConfigVersion.cmake
-        DESTINATION lib${LIB_SUFFIX}/vigra)
+        DESTINATION lib${LIB_SUFFIX}/cmake/vigra)
 EXPORT(TARGETS vigraimpex FILE vigra-targets.cmake)
 
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