fixed include search paths

Former-commit-id: 3d478a27e67c5d8b22e66d761490d13b2cf43bf3

tutorial/cmake/FindGLEW.cmake

@@ -6,8 +6,10 @@
 #  GLEW_SOURCES - the GLEW source file list
 
 FIND_PATH(GLEW_INCLUDE_DIR GL/glew.h
-   ${PROJECT_SOURCE_DIR}/../../external/glew/include
-   ${PROJECT_SOURCE_DIR}/../external/glew/include
+   ${PROJECT_SOURCE_DIR}/../../../external/nanogui/ext/glew/include
+   ${PROJECT_SOURCE_DIR}/../../external/nanogui/ext/glew/include
+   ${PROJECT_SOURCE_DIR}/../external/nanogui/ext/glew/include
+   ${PROJECT_SOURCE_DIR}/external/nanogui/ext/glew/include
    ${PROJECT_SOURCE_DIR}/../../../libigl/external/nanogui/ext/glew/include
    ${PROJECT_SOURCE_DIR}/../../libigl/external/nanogui/ext/glew/include
    ${PROJECT_SOURCE_DIR}/../libigl/external/nanogui/ext/glew/include