fix(generator): handle preview version pkg name (#3511)

Author: noahdietz

google-api-go-generator/gen.go

@@ -467,6 +467,9 @@ func renameVersion(version string) string {
 	if version == "alpha" || version == "beta" {
 		return "v0." + version
 	}
+	if version == "preview" {
+		return "v1.preview"
+	}
 	if m := oddVersionRE.FindStringSubmatch(version); m != nil {
 		return m[1] + "/" + m[2]
 	}

google-api-go-generator/gen_test.go

@@ -237,6 +237,18 @@ func TestRenameVersion(t *testing.T) {
 			version: "my_api_v1.2",
 			want:    "my_api/v1.2",
 		},
+		{
+			version: "alpha",
+			want:    "v0.alpha",
+		},
+		{
+			version: "beta",
+			want:    "v0.beta",
+		},
+		{
+			version: "preview",
+			want:    "v1.preview",
+		},
 	}
 	for _, test := range tests {
 		if got := renameVersion(test.version); got != test.want {