build(deps): bump idna from 2.9 to 2.10

Bumps [idna](https://github.com/kjd/idna) from 2.9 to 2.10.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.rst)
- [Commits](kjd/idna@v2.9...v2.10)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements-pinned.txt

@@ -4,7 +4,7 @@ chardet==3.0.4            # via requests
 colorama==0.4.3           # via securesystemslib
 cryptography==2.9.2         # via securesystemslib
 enum34==1.1.6             ; python_version < '3' # via cryptography
-idna==2.9                 # via requests
+idna==2.10                 # via requests
 ipaddress==1.0.23         ; python_version < '3' # via cryptography
 iso8601==0.1.12
 pycparser==2.20           # via cffi