Minor: Resolved this warning associated with a "Non-Standard" default

[martinfrances107]

When I looked at the warning, I noted that everything could be auto derived.

warning: method `default` can be confused for the standard trait method `std::default::Default::default`
   --> plotters-backend/src/text.rs:120:9
    |
120 | /         pub fn default() -> Self {
121 | |             Pos {
122 | |                 h_pos: HPos::Left,
123 | |                 v_pos: VPos::Top,
124 | |             }
125 | |         }
    | |_________^
    |
    = help: consider implementing the trait `std::default::Default` or choosing a less ambiguous method name
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#should_implement_trait
    = note: `#[warn(clippy::should_implement_trait)]` on by default

[AaronErhardt]

Thanks!