Fix typo in an OID name

fixes #314
diff --git a/library/oid.c b/library/oid.c
index b616d7e..682b845 100644
--- a/library/oid.c
+++ b/library/oid.c
@@ -268,7 +268,7 @@
         EXT_KEY_USAGE,
     },
     {
-        { ADD_LEN( OID_EXTENDED_KEY_USAGE ),   "id-ce-keyUsage",           "Extended Key Usage" },
+        { ADD_LEN( OID_EXTENDED_KEY_USAGE ),   "id-ce-extKeyUsage",        "Extended Key Usage" },
         EXT_EXTENDED_KEY_USAGE,
     },
     {