Fix version number in glfwGetMonitorWorkarea docs

Related to #1322.
diff --git a/include/GLFW/glfw3.h b/include/GLFW/glfw3.h
index 623ae76..2abad17 100644
--- a/include/GLFW/glfw3.h
+++ b/include/GLFW/glfw3.h
@@ -1952,7 +1952,7 @@
  *
  *  @sa @ref monitor_properties
  *
- *  @since Added in version 3.0.
+ *  @since Added in version 3.3.
  *
  *  @ingroup monitor
  */