webpmux.1: correct grammar

argument -> arguments

Change-Id: I57132c942150f18dccc5ef84c4c09a6dcc054ffa
diff --git a/man/webpmux.1 b/man/webpmux.1
index eb41a61..3afa602 100644
--- a/man/webpmux.1
+++ b/man/webpmux.1
@@ -1,5 +1,5 @@
 .\"                                      Hey, EMACS: -*- nroff -*-
-.TH WEBPMUX 1 "December 1, 2017"
+.TH WEBPMUX 1 "April 23, 2018"
 .SH NAME
 webpmux \- create animated WebP files from non\-animated WebP images, extract
 frames from animated WebP images, and manage XMP/EXIF metadata and ICC profile.
@@ -58,7 +58,7 @@
 \fBwebpmux\fP can be used to create/extract from animated WebP files, as well as
 to add/extract/strip XMP/EXIF metadata and ICC profile.
 If a single file name (not starting with the character '\-') is supplied as
-the argument, the command line argument are actually tokenized from this file.
+the argument, the command line arguments are actually tokenized from this file.
 This allows for easy scripting or using large number of arguments.
 .SH OPTIONS
 .SS GET_OPTIONS (\-get):