requirements: update toposort requirement from <1.7 to <1.8

Updates the requirements on [toposort]() to permit the latest version.

---
updated-dependencies:
- dependency-name: toposort
  dependency-type: direct:production
...

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

requirements.txt

@@ -11,7 +11,7 @@ networkx<2.6
 numpy<1.21.3
 pillow<8.4.0
 pint<0.18
-toposort<1.7
+toposort<1.8
 torch>=1.8.0, <2.0.0; (platform_machine == 'AMD64' or platform_machine == 'x86_64') and platform_python_implementation == 'CPython' and implementation_name == 'cpython'
 typecheck-decorator<=1.2
 leabra-psyneulink<=0.3.2