Fix gocognit output when a function has generic receiver type

recvString func in gocognit returns BADRECV when the function's receiver is a
generic type.

gocognit.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/token"
+	"strings"
 
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
@@ -57,6 +58,15 @@ func recvString(recv ast.Expr) string {
 		return t.Name
 	case *ast.StarExpr:
 		return "*" + recvString(t.X)
+	case *ast.IndexExpr:
+		return recvString(t.X) + "[" + recvString(t.Index) + "]"
+	case *ast.IndexListExpr:
+		targs := make([]string, 0, len(t.Indices))
+		for _, exp := range t.Indices {
+			targs = append(targs, recvString(exp))
+		}
+
+		return recvString(t.X) + "[" + strings.Join(targs, ", ") + "]"
 	}
 	return "BADRECV"
 }