Bump httpie from 1.0.3 to 3.1.0 in /requirements

Bumps [httpie](https://github.com/httpie/httpie) from 1.0.3 to 3.1.0.
- [Release notes](https://github.com/httpie/httpie/releases)
- [Changelog](https://github.com/httpie/httpie/blob/master/CHANGELOG.md)
- [Commits](httpie/cli@1.0.3...3.1.0)

---
updated-dependencies:
- dependency-name: httpie
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/dev.txt

@@ -3,7 +3,7 @@ ForgeryPy==0.1
 Pygments==2.7.4
 colorama==0.3.9
 coverage==4.4.1
-httpie==1.0.3
+httpie==3.1.0
 requests==2.20.0
 selenium==3.5.0
 unittest-xml-reporting==2.1.0