CMake: Fix typo in GLFW detection

Let it be noted I utterly dislike their syntax.

utils.cmake

@@ -38,7 +38,7 @@ endif()
 
 if(WITH_SYSTEM_GLFW STREQUAL "ON")
     find_package(glfw3 3.2.1 REQUIRED)
-else(WITH_SYSTEM_GLFW STREQUAL "IF_POSSIBLE")
+elseif(WITH_SYSTEM_GLFW STREQUAL "IF_POSSIBLE")
     find_package(glfw3 3.2.1)
 endif()
 if (glfw3_FOUND)