Fix warning

This is a bug in R ... but I don't want warnings.
```
  Author field differs from that derived from Authors@R
    Author:    ‘Jeffrey B. Arnold [aut, cre] (<https://orcid.org/0000-0001-9953-3904>), Gergely Daroczi [ctb], Bo Werth [ctb], Brian Weitzner [ctb], Joshua Kunst [ctb], Baptise Auguie [ctb], Bob Rudis [ctb], Hadley Wickham [ctb] (Code from the ggplot2 package.), Justin Talbot [ctb] (Code from the labeling package), Joshua London [ctb]’
    Authors@R: ‘Jeffrey B. Arnold [aut, cre] (0000-0001-9953-3904), Gergely Daroczi [ctb], Bo Werth [ctb], Brian Weitzner [ctb], Joshua Kunst [ctb], Baptise Auguie [ctb], Bob Rudis [ctb], Hadley Wickham [ctb] (Code from the ggplot2 package.), Justin Talbot [ctb] (Code from the labeling package), Joshua London [ctb]’
```

DESCRIPTION

@@ -2,7 +2,8 @@ Package: ggthemes
 Version: 4.1.0
 Title: Extra Themes, Scales and Geoms for 'ggplot2'
 Authors@R: c(person("Jeffrey B.", "Arnold", role = c("aut", "cre"),
-    email = "jeffrey.arnold@gmail.com", comment = c(ORCID = "0000-0001-9953-3904")),
+    email = "jeffrey.arnold@gmail.com", 
+    comment = "<https://orcid.org/0000-0001-9953-3904>"),
     person("Gergely", "Daroczi", role = "ctb"),
     person("Bo", "Werth", role = "ctb"),
     person("Brian", "Weitzner", role = "ctb"),