Bug 41327: Silence Sass deprecation warnings

Some warning are about issue we can address (legacy-js-api for
instance), and others we have to wait to be fixed in Bootstrap
(color-functions, global-builtin).

For now I think we should silence these warnings.

To test, apply the patch and run 'yarn build.' There should be no
warnings.

Sponsored-by: Athens County Public Libraries
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>

gulpfile.js

@@ -32,6 +32,12 @@ var CSS_BASE = args.view == "opac" ? OPAC_CSS_BASE : STAFF_CSS_BASE;
 
 var sassOptions = {
     importer: tildeImporter,
+    silenceDeprecations: [
+        "color-functions",
+        "global-builtin",
+        "import",
+        "legacy-js-api",
+    ],
     includePaths: [__dirname + "/node_modules", __dirname + "/../node_modules"],
 };