replace nonexistent option in `--help` output (#372)

Recently, I noticed that  the 'after_help' text mentions a `number` op-
tion, which doen't seem to be implemented.

Let's fix this.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/cli.rs b/src/cli.rs
index 57ea19d8..e762fc38 100644
--- a/src/cli.rs
+++ b/src/cli.rs
@@ -34,7 +34,7 @@ given in a git config file, using the usual option names but without the initial
 is
 
 [delta]
-    number = true
+    line-numbers = true
     zero-style = dim syntax
 
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