Fixed build warnings

src/headless.rs

@@ -106,26 +106,27 @@ impl gl_common::GlFunctionsSource for HeadlessContext {
 
 impl GlContext for HeadlessContext {
     unsafe fn make_current(&self) {
-        self.make_current()
+        self.context.make_current()
     }
 
     fn is_current(&self) -> bool {
-        self.is_current()
+        self.context.is_current()
     }
 
     fn get_proc_address(&self, addr: &str) -> *const libc::c_void {
-        self.get_proc_address(addr)
+        self.context.get_proc_address(addr)
     }
 
     fn swap_buffers(&self) {
-        self.swap_buffers()
+        self.context.swap_buffers()
     }
 
     fn get_api(&self) -> Api {
-        self.get_api()
+        self.context.get_api()
     }
 
     fn get_pixel_format(&self) -> PixelFormat {
-        self.get_pixel_format()
+        self.context.get_pixel_format()
     }
 }
+