Fallback to maven central for artifacts such as sources or javadocs that are not mirrored on Mojang's repo.

Fixes #1032

src/main/java/net/fabricmc/loom/LoomRepositoryPlugin.java

@@ -117,6 +117,10 @@ public class LoomRepositoryPlugin implements Plugin<PluginAware> {
 				sources.artifact();
 				sources.ignoreGradleMetadataRedirection();
 			});
+
+			// Fallback to maven central for artifacts such as sources or javadocs that are not mirrored on Mojang's repo.
+			// See: https://github.com/FabricMC/fabric-loom/issues/1032
+			repo.artifactUrls(ArtifactRepositoryContainer.MAVEN_CENTRAL_URL);
 		});
 	}