[BUG] example crash under centos 7.5

[skydig]

Describe the bug
Describe what is expected, what you actually get.
It would be nice to have screenshot or result image uploaded

To Reproduce

Sstack backtrace:
0: rust_begin_unwind
at /rustc/8df7e723ea729a7f917501cc2d91d640b7021373/library/std/src/panicking.rs:646:5
1: core::panicking::panic_nounwind_fmt::runtime
at /rustc/8df7e723ea729a7f917501cc2d91d640b7021373/library/core/src/panicking.rs:110:18
2: core::panicking::panic_nounwind_fmt
at /rustc/8df7e723ea729a7f917501cc2d91d640b7021373/library/core/src/panicking.rs:120:5
3: core::panicking::panic_nounwind
at /rustc/8df7e723ea729a7f917501cc2d91d640b7021373/library/core/src/panicking.rs:215:5
4: core::slice::raw::from_raw_parts::precondition_check
at /rustc/8df7e723ea729a7f917501cc2d91d640b7021373/library/core/src/ub_checks.rs:66:21
5: core::slice::raw::from_raw_parts
at /rustc/8df7e723ea729a7f917501cc2d91d640b7021373/library/core/src/slice/raw.rs:96:9
6: font_kit::loaders::freetype::Font::rasterize_glyph
at /home/alcatel/.cargo/registry/src/index.crates.io-6f17d22bba15001f/font-kit-0.11.0/src/loaders/freetype.rs:847:26
7: <plotters::style::font::ttf::FontDataInternal as plotters::style::font::FontData>::draw
at ./src/style/font/ttf.rs:265:26
8: plotters::style::font::font_desc::FontDesc::draw
at ./src/style/font/font_desc.rs:168:29
9: <plotters::style::text::TextStyle as plotters_backend::text::BackendTextStyle>::draw
at ./src/style/text.rs:322:9
10: plotters_backend::DrawingBackend::draw_text
at /home/alcatel/plotters/plotters-backend/src/lib.rs:250:15
11: plotters::drawing::area::DrawingArea<DB,plotters::coord::Shift>::titled::{{closure}}
at ./src/drawing/area.rs:496:13
12: plotters::drawing::area::DrawingArea<DB,CT>::backend_ops
at ./src/drawing/area.rs:282:13
13: plotters::drawing::area::DrawingArea<DB,plotters::coord::Shift>::titled
at ./src/drawing/area.rs:495:9
14: chart::main
at ./examples/chart.rs:9:21
15: core::ops::function::FnOnce::call_once
at /rustc/8df7e723ea729a7f917501cc2d91d640b7021373/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with RUST_BACKTRACE=full for a verbose backtrace.
thread caused non-unwinding panic. aborting.

Version Information
Please give us what version you are using. If you are pulling Plotters directly from git repo, please mention this as well

[skydig]

after upgrade
ttf-parser = { version = "0.18", optional = true }
font-kit = { version = "0.13", optional = true }
crash disappear. I make a pullrequest, and close this report