Documentation: Combine export commands

Author: sanssecours

README.MacOSX

@@ -69,8 +69,7 @@ Download the latest version of GLEW from
 https://github.com/nigels-com/glew/releases. Extract the package, and then
 build it with the following commands:
 
-$ export MACOSX_DEPLOYMENT_TARGET=10.9
-$ export GLEW_DEST=/usr/local
+$ export MACOSX_DEPLOYMENT_TARGET=10.9 GLEW_DEST=/usr/local
 $ make SYSTEM=darwin-universal glew.lib.static
 $ sudo make install.include
 $ sudo cp lib/libGLEW.a /usr/local/lib