Improve example for regex (pipe-cd#4644)

Signed-off-by: 鈴木 優耀 <suzuki_masaaki@cyberagent.co.jp>

docs/content/en/docs-v0.45.x/user-guide/configuration-reference.md

@@ -198,7 +198,7 @@ One of `yamlField` or `regex` is required.
 |-|-|-|-|
 | file | string | The relative path from the repository root to the file to be updated. | Yes |
 | yamlField | string | The yaml path to the field to be updated. It requires to start with `$` which represents the root element. e.g. `$.foo.bar[0].baz`. | No |
-| regex | string | The regex string that specify what should be replaced. The only first capturing group enclosed by `()` will be replaced with the new value. e.g. `host.xz/foo/bar:(v[0-9].[0-9].[0-9])` | No |
+| regex | string | The regex string that specify what should be replaced. The only first capturing group enclosed by `()` will be replaced with the new value. e.g. `host.xz/foo/bar:(v[0-9]+.[0-9]+.[0-9]+)` | No |
 
 ## CommitMatcher