fix captialization issue in CMakeLists.txt
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1a344bd..1fe3fdc 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -28,7 +28,7 @@
 set(Python_ADDITIONAL_VERSIONS 3.4 3.5 3.6 3.7)
 if (NOT ${PYBIND11_PYTHON_VERSION} STREQUAL "")
   find_package(PythonLibs ${PYBIND11_PYTHON_VERSION} EXACT)
-  if (NOT PythonLibs_FOUND)
+  if (NOT PYTHONLIBS_FOUND)
     find_package(PythonLibs ${PYBIND11_PYTHON_VERSION} REQUIRED)
   endif()
 else()
diff --git a/docs/cmake.rst b/docs/cmake.rst
index 0298303..d405bc3 100644
--- a/docs/cmake.rst
+++ b/docs/cmake.rst
@@ -48,7 +48,7 @@
     set(Python_ADDITIONAL_VERSIONS 3.4 3.5 3.6 3.7)
     if (NOT ${EXAMPLE_PYTHON_VERSION} STREQUAL "")
       find_package(PythonLibs ${EXAMPLE_PYTHON_VERSION} EXACT)
-      if (NOT PythonLibs_FOUND)
+      if (NOT PYTHONLIBS_FOUND)
         find_package(PythonLibs ${EXAMPLE_PYTHON_VERSION} REQUIRED)
       endif()
     else()