BUG: fix cmake variable name

CMake/otbIncludeDirectories.cmake

@@ -108,7 +108,7 @@ ENDIF(OTB_USE_EXTERNAL_TINYXML)
 
 IF(OTB_USE_EXTERNAL_MUPARSER)
   SET(OTB_INCLUDE_DIRS_BUILD_TREE ${OTB_INCLUDE_DIRS_BUILD_TREE}
-      ${MUPARSER_INCLUDE_DIRS})
+      ${MUPARSER_INCLUDE_DIR})
 ELSEIF(OTB_USE_EXTERNAL_MUPARSER)
   SET(OTB_INCLUDE_DIRS_BUILD_TREE ${OTB_INCLUDE_DIRS_BUILD_TREE}
       ${OTB_SOURCE_DIR}/Utilities/otbmuparser)
@@ -374,7 +374,7 @@ ENDIF(OTB_USE_EXTERNAL_TINYXML)
 #For MuParser header file
 IF(OTB_USE_EXTERNAL_MUPARSER)
         SET(OTB_INCLUDE_ABSOLUE_DIRS ${OTB_INCLUDE_ABSOLUE_DIRS}
-                ${MUPARSER_INCLUDE_DIRS})
+                ${MUPARSER_INCLUDE_DIR})
 ELSE(OTB_USE_EXTERNAL_MUPARSER)
         SET(OTB_INCLUDE_RELATIVE_DIRS ${OTB_INCLUDE_RELATIVE_DIRS}
                 Utilities/otbmuparser)