fix partial matrix excludes

the docs clearly state that excludes only have to match on the
keys provided: https://docs.travis-ci.com/user/build-matrix/#excluding-jobs

lib/wwtd.rb

@@ -117,7 +117,9 @@ def matrix(config)
 
       if matrix_config = config.delete("matrix")
         if exclude = matrix_config["exclude"]
-          matrix -= exclude
+          exclude.each do |exclude_cell|
+            matrix.delete_if { |cell| matrix_match?(cell, exclude_cell) }
+          end
         end
         if include = matrix_config["include"]
           if matrix == [{}]
@@ -130,6 +132,10 @@ def matrix(config)
       matrix.map! { |c| config.merge(c) }
     end
 
+    def matrix_match?(cell, exclude)
+      cell.slice(*exclude.keys) == exclude
+    end
+
     def with_clean_env(&block)
       if defined?(Bundler)
         Bundler.with_clean_env(&block)

spec/wwtd_spec.rb

@@ -593,6 +593,23 @@ def call(config)
         {"rvm"=>"c", "gemfile"=>"Gemfile1"},
       ]
     end
+
+    it "excludes partial matches" do
+      call(
+        "gemfile" => ["Gemfile1", "Gemfile2"],
+        "rvm" => ["a", "b"],
+        "env" => ["KEY=val"],
+        "matrix" => {
+          "exclude" => [
+            {"gemfile" => "Gemfile1", "rvm" => "b"}
+          ],
+        }
+      ).should == [
+        {"rvm" => "a", "gemfile"=>"Gemfile1", "env" => "KEY=val"},
+        {"rvm" => "a", "gemfile"=>"Gemfile2", "env" => "KEY=val"},
+        {"rvm" => "b", "gemfile"=>"Gemfile2", "env" => "KEY=val"},
+      ]
+    end
   end
 
   describe ".config_info" do