Fix typos in ensmallen configuration.

CMake/FindEnsmallen.cmake

@@ -3,7 +3,7 @@
 #
 # This module sets the following variables:
 #  ENSMALLEN_FOUND - set to true if the library is found
-#  ENSMALLEN_INCLUDE_DIRS - list of required include directories
+#  ENSMALLEN_INCLUDE_DIR - list of required include directories
 #  ENSMALLEN_VERSION_MAJOR - major version number
 #  ENSMALLEN_VERSION_MINOR - minor version number
 #  ENSMALLEN_VERSION_PATCH - patch version number

CMakeLists.txt

@@ -346,7 +346,7 @@ ${ENS_DOWNLOAD_ERROR}!  Error log: ${ENS_DOWBLOAD_LOG}")
     endif ()
   endif ()
 else ()
-  set(MLPACK_INCLUDE_DIRS ${MLPACK_INCLUDE_DIRS} ${ENSMALLEN_INCLUDE_DIRS})
+  set(MLPACK_INCLUDE_DIRS ${MLPACK_INCLUDE_DIRS} "${ENSMALLEN_INCLUDE_DIR}")
 endif ()
 
 # Unfortunately this configuration variable is necessary and will need to be