Change scale number type: `f64` to `f32`
Change scale number type: `f64` to `f32`

SDL2 uses `float` for `SDL_RendererGetScale()`, so `f32` is used to
avoid unnecessary casting.

caldwell/rust-sdl2,nukep/rust-sdl2,bvssvni/rust-sdl2,Rust-SDL2/rust-sdl2,bfops/rust-sdl2,beni55/rust-sdl2,vadixidav/rust-sdl2,Cobrand/rust-sdl2,tempbottle/rust-sdl2,crumblingstatue/rust-sdl2,Rust-SDL2/rust-sdl2,Rust-SDL2/rust-sdl2,oldmanmike/rust-sdl2,wilsoniya/rust-sdl2,inrustwetrust/rust-sdl2,Cobrand/rust-sdl2,Cobrand/rust-sdl2,AngryLawyer/rust-sdl2,PistonDevelopers/rust-sdl2