Bump minimum version of Hugo to 0.38 (#581)

Recent commit 7f744f0 used `.Site.IsServer`, which is added in Hugo v0.38

theme.toml

@@ -3,7 +3,7 @@ license = "MIT"
 licenselink = "https://github.com/gcushen/hugo-academic/blob/master/LICENSE.md"
 description = "Easily create beautifully simple academic or personal sites"
 homepage = "https://github.com/gcushen/hugo-academic"
-min_version = 0.30
+min_version = 0.38
 tags = ["academic",
         "portfolio",
         "responsive",