Fix some typos in ch02-02-timers.md

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (6e276f6) 86.39% compared to head (c3512d3) 85.44%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #162 +/- ## ========================================== - Coverage 86.39% 85.44% -0.96% ========================================== Files 16 14 -2 Lines 1941 1759 -182 ========================================== - Hits 1677 1503 -174 + Misses 264 256 -8 ``` | [Flag](https://app.codecov.io/gh/Smithay/calloop/pull/162/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay) | Coverage Δ | | |---|---|---| | [macos-latest](https://app.codecov.io/gh/Smithay/calloop/pull/162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay) | `?` | | | [ubuntu-latest](https://app.codecov.io/gh/Smithay/calloop/pull/162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#carryforward-flags-in-the-pull-request-comment) to find out more. [see 4 files with indirect coverage changes](https://app.codecov.io/gh/Smithay/calloop/pull/162/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay)

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[elinorbgr]

Thanks!