cmake revert change to linux so

Put back the stanza fixing the .so name to what it has always been
on Linux, trashed in f1b12544

Signed-off-by: Andy Green <andy.green@linaro.org>

CMakeLists.txt

@@ -444,6 +444,10 @@ elseif(APPLE)
 	if (LWS_WITH_SHARED)
 		set_property(TARGET websockets_shared PROPERTY MACOSX_RPATH YES)
 	endif()
+else()
+	set_target_properties(websockets_shared
+	PROPERTIES
+	OUTPUT_NAME websockets)
 endif()
 
 # Set the so version of the lib.