pgm: Fix misspelled key of an externalized string

Bug: 502107
Change-Id: I76d0981c8463b63bd049f50cdc7d549fa0604b3c
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/Clean.java

@@ -50,7 +50,7 @@ import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.pgm.internal.CLIText;
 import org.kohsuke.args4j.Option;
 
-@Command(common = true, usage = "usage_clean")
+@Command(common = true, usage = "usage_Clean")
 class Clean extends TextBuiltin {
 	@Option(name = "-d", usage = "usage_removeUntrackedDirectories")
 	private boolean dirs = false;