fix: use correct mimetypes for .pem and .pub (#1891)

This changes the .pem mimetype to application/x-pem-file. It also
changes the .pub mimetype to text/plain. Lastly, it updates
textApplicationMimetypes with this change.

frontend/app/view/preview/preview.tsx

@@ -74,8 +74,8 @@ const SpecializedViewMap: { [view: string]: ({ model }: SpecializedViewProps) =>
 
 const textApplicationMimetypes = [
     "application/sql",
-    "application/pem-certificate-chain",
     "application/x-php",
+    "application/x-pem-file",
     "application/x-httpd-php",
     "application/liquid",
     "application/graphql",

pkg/util/fileutil/mimetypes.go

@@ -128,7 +128,6 @@ var StaticMimeTypeMap = map[string]string{
 	".relo":                      "application/p2p-overlay+xml",
 	".pdf":                       "application/pdf",
 	".pdx":                       "application/PDX",
-	".pem":                       "application/pem-certificate-chain",
 	".pgp":                       "application/pgp-encrypted",
 	".asc":                       "application/pgp-keys",
 	".sig":                       "application/pgp-signature",
@@ -351,7 +350,6 @@ var StaticMimeTypeMap = map[string]string{
 	".ecig":                      "application/vnd.evolv.ecig.settings",
 	".ecigtheme":                 "application/vnd.evolv.ecig.theme",
 	".mpw":                       "application/vnd.exstream-empower+zip",
-	".pub":                       "application/vnd.exstream-package",
 	".ez2":                       "application/vnd.ezpix-album",
 	".ez3":                       "application/vnd.ezpix-package",
 	".gdz":                       "application/vnd.familysearch.gedcom+zip",
@@ -769,6 +767,7 @@ var StaticMimeTypeMap = map[string]string{
 	".gtar":                      "application/x-gtar",
 	".tgz":                       "application/x-gtar-compressed",
 	".hdf":                       "application/x-hdf",
+	".pem":                       "application/x-pem-file",
 	".php":                       "application/x-php",
 	".hwp":                       "application/x-hwp",
 	".ica":                       "application/x-ica",
@@ -1116,6 +1115,7 @@ var StaticMimeTypeMap = map[string]string{
 	".n3":                        "text/n3",
 	".txt":                       "text/plain",
 	".conf":                      "text/plain",
+	".pub":                       "text/plain",
 	".awk":                       "text/x-awk",
 	".provn":                     "text/provenance-notation",
 	".rst":                       "text/prs.fallenstein.rst",