Update structopt requirement from 0.2.18 to 0.3.26

[dependabot]

Updates the requirements on structopt to permit the latest version.

Changelog

Sourced from structopt's changelog.

v0.3.25 (2021-10-18)

• Fix duplication of aliases in subcommands #504

v0.3.25 (2021-10-18)

• No changes

v0.3.23 (2021-08-30)

• Update minimal rust version to 1.46 because of bitflags 1.3
• Fixed a bug that occurs when the type of map becomes ambiguous.
• Add support for skip for enum variant subcommands

v0.3.22 (2021-07-04)

• Add support for generics in derive

v0.3.21 (2020-11-30)

• Fixed another breakage when the struct is placed inside a macro_rules! macro.

v0.3.20 (2020-10-12)

• Fixed a breakage when the struct is placed inside a macro_rules! macro.

v0.3.19 (2020-10-08)

• Added StructOpt::from_args_safe as a shortcut for StructOpt::from_iter_safe(std::env::args_os()).
• Some links in documentation have been corrected.

v0.3.18 (2020-09-23)

• Unsafe code has been forbidden. This makes cargo geiger list structopt as "safe". Maybe it will help somebody trying to locate a bug in their dependency tree.

v0.3.17 (2020-08-25)

• Fixed a breakage with resent rustc versions due to quote_spanned misuse.

v0.3.16 (2020-08-05)

• Added the new example.
• Allow #[structopt(flatten)] fields to have doc comments. The comments are ignored.
• The paw crate is now being reexported when paw feature is enabled, see [#407](https://github.com/TeXitoi/structopt/issues/407).

... (truncated)

Commits

• 97e92a3 v0.3.26
• 2bdd6b4 Clarification on maintenance since clap v3 is out
• 2736281 Upgrade heck
• 358cccf [docs] Add output to all examples
• 4c1a8fc Link to the clap API in the documentation that says all clap methods can be used
• ffd4772 Typo
• da1fff8 v0.3.25
• e83b0fc Merge branch 'master' of github.com:TeXitoi/structopt
• 6dc2963 v0.4.17
• ddb51cb Fix duplication of aliases in subcommands
• Additional commits viewable in compare view

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