command tests looked for providers in the graphs

The quotes in provider names needs to be escaped, so these tests were
looking for the wrong output to begin with.

command/graph_test.go

@@ -33,7 +33,7 @@ func TestGraph(t *testing.T) {
 	}
 
 	output := ui.OutputWriter.String()
-	if !strings.Contains(output, `provider["registry.terraform.io/hashicorp/test"]`) {
+	if !strings.Contains(output, `provider[\"registry.terraform.io/hashicorp/test\"]`) {
 		t.Fatalf("doesn't look like digraph: %s", output)
 	}
 }
@@ -80,7 +80,7 @@ func TestGraph_noArgs(t *testing.T) {
 	}
 
 	output := ui.OutputWriter.String()
-	if !strings.Contains(output, `provider["registry.terraform.io/hashicorp/test"]`) {
+	if !strings.Contains(output, `provider[\"registry.terraform.io/hashicorp/test\"]`) {
 		t.Fatalf("doesn't look like digraph: %s", output)
 	}
 }
@@ -161,7 +161,7 @@ func TestGraph_plan(t *testing.T) {
 	}
 
 	output := ui.OutputWriter.String()
-	if !strings.Contains(output, `provider["registry.terraform.io/hashicorp/test"]`) {
+	if !strings.Contains(output, `provider[\"registry.terraform.io/hashicorp/test\"]`) {
 		t.Fatalf("doesn't look like digraph: %s", output)
 	}
 }