fix: Fix reference to 3rd party styles in stylesheets.

Since latest scss build tools which became available in
`@patternslib/dev` version 3.6 references to `node_modules` need to be
left out. The build tool searches in node_modules anyways. This is now
fixed.

Author: thet

src/pat/colour-picker/_colour-picker.scss

@@ -1,5 +1,6 @@
 @charset "UTF-8";
-@import "node_modules/spectrum-colorpicker/spectrum";
+
+@import "spectrum-colorpicker/spectrum";
 
 .checkNative,
 .checkPattern {

src/pat/date-picker/_date-picker.scss

@@ -1,2 +1,2 @@
 @charset "UTF-8";
-@import "node_modules/pikaday/scss/pikaday.scss";
+@import "pikaday/scss/pikaday.scss";