Drop dimod 0.8.x support

Version 0.8 is now almost 2 years old, and most Ocean packages already
dropped support for it, so it's becoming a pain to maintain the whole
collection of packages compatible (primarily samplers: neal, tabu,
greedy) and tested.

.circleci/config.yml

@@ -192,7 +192,10 @@ workflows:
           matrix:
             parameters:
               python-version: &python-versions ["3.6.12", "3.7.9", "3.8.6", "3.9.0"]
-              dimod-version: ["~=0.8.0,>=0.8.11", "~=0.9.0", "~=0.10.0,>0.10.4"]
+              dimod-version: ["==0.9.0", "~=0.9.0", "~=0.10.0,>0.10.4"]
+            exclude:
+              - python-version: "3.9.0"
+                dimod-version: "==0.9.0"    # py39 not supported until 0.9.11
 
       - test-macos:
           name: test-macos-py<< matrix.python-version >>

setup.py

@@ -12,7 +12,7 @@
 
 # Package requirements, minimal pinning
 install_requires = ['numpy>=1.15.0', 'networkx', 'click>5', 'plucky>=0.4.3',
-                    'dimod>=0.8.11,<0.11,!=0.10.0,!=0.10.1,!=0.10.2,!=0.10.3,!=0.10.4',
+                    'dimod>=0.9.0,<0.11,!=0.10.0,!=0.10.1,!=0.10.2,!=0.10.3,!=0.10.4',
                     'minorminer>=0.1.7', 'dwave-networkx>=0.6.6', 'dwave-system>=0.7.6',
                     'dwave-neal>=0.5.1', 'dwave-tabu>=0.2.0', 'dwave-greedy>=0.1.0']