Remove redundant mention of Maven in Gradle plugin (#4068)

Co-authored-by: Mridula <[email protected]>

jib-gradle-plugin/README.md

@@ -314,7 +314,7 @@ The following table contains additional system properties that are not available
 Property | Type | Default | Description
 --- | --- | --- | ---
 `jib.httpTimeout` | `int` | `20000` | HTTP connection/read timeout for registry interactions, in milliseconds. Use a value of `0` for an infinite timeout.
-`jib.useOnlyProjectCache` | `boolean` | `false` | If set to true, Jib does not share a cache between different Maven projects.
+`jib.useOnlyProjectCache` | `boolean` | `false` | If set to true, Jib does not share a cache between different Gradle projects.
 `jib.baseImageCache` | `File` | *Platform-dependent*\*\*\* | Sets the directory to use for caching base image layers. This cache can (and should) be shared between multiple images.
 `jib.applicationCache` | `File` | `[project dir]/build/jib-cache` | Sets the directory to use for caching application layers. This cache can be shared between multiple images.
 `jib.console` | `String` | *None* | If set to `plain`, Jib will print plaintext log messages rather than display a progress bar during the build.