Changed ticks function from &mut self to &self.

changelog.md

@@ -4,6 +4,7 @@ when upgrading from a version of rust-sdl2 to another.
 ### Unreleased
 
  * Add patch to fix metal detection (https://bugzilla.libsdl.org/show_bug.cgi?id=4988)
+ * Changed signature of `TimerSubsystem::ticks to accept `&self`.
 
 ### v0.34.3
 

src/sdl2/timer.rs

@@ -31,7 +31,7 @@ impl TimerSubsystem {
     /// Gets the number of milliseconds elapsed since the timer subsystem was initialized.
     ///
     /// It's recommended that you use another library for timekeeping, such as `time`.
-    pub fn ticks(&mut self) -> u32 {
+    pub fn ticks(&self) -> u32 {
         // Google says this is probably not thread-safe (TODO: prove/disprove this).
         unsafe { sys::SDL_GetTicks() }
     }