remove "shared" default cmake. less confusing for new users

Working-on-GNU-Linux.md

@@ -150,7 +150,7 @@ Instead of using the embedded GLFW, you can download GLFW3 and build it from sou
     wget https://github.com/glfw/glfw/releases/download/3.2.1/glfw-3.2.1.zip
     unzip glfw-3.2.1.zip
     cd glfw-3.2.1
-    cmake -DBUILD_SHARED_LIBS=ON
+    cmake
     sudo make install
 
 Now with GLFW installed, you may build raylib while specifying `USE_EXTERNAL_GLFW`: