Bump coincurve from 14.0.0 to 15.0.0 in /requirements

Bumps [coincurve](https://github.com/ofek/coincurve) from 14.0.0 to 15.0.0.
- [Release notes](https://github.com/ofek/coincurve/releases)
- [Changelog](https://github.com/ofek/coincurve/blob/master/docs/history.md)
- [Commits](ofek/coincurve@v14.0.0...v15.0.0)

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

Author: dependabot[bot]

requirements/requirements-ci.txt

@@ -130,7 +130,7 @@ click==8.0.0a1
     #   flask
     #   pip-tools
     #   raiden-contracts
-coincurve==14.0.0
+coincurve==15.0.0
     # via
     #   -r requirements-dev.txt
     #   raiden-contracts

requirements/requirements-dev.txt

@@ -110,7 +110,7 @@ click==8.0.0a1
     #   flask
     #   pip-tools
     #   raiden-contracts
-coincurve==14.0.0
+coincurve==15.0.0
     # via
     #   -r requirements.txt
     #   raiden-contracts

requirements/requirements.txt

@@ -37,7 +37,7 @@ click==8.0.0a1
     #   -r requirements.in
     #   flask
     #   raiden-contracts
-coincurve==14.0.0
+coincurve==15.0.0
     # via
     #   -r requirements.in
     #   raiden-contracts