Copy-pasta error from NNG for coverage.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index b0aa665..a0446b1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -115,7 +115,7 @@
     set(NN_WARN_FLAGS "-Wall -Wextra")
 endif()
 
-if (NNG_ENABLE_COVERAGE)
+if (NN_ENABLE_COVERAGE)
     # NB: This only works for GCC and Clang 3.0 and newer.  If your stuff
     # is older than that, you will need to find something newer.  For
     # correct reporting, we always turn off all optimizations.