Fixing less @import paths in auth/base/tree.

These paths were problematic for --NotebookApp.use_less=True mode.

IPython/html/static/auth/less/style.less

@@ -1,2 +1,2 @@
-@import "../auth/less/login.less";
-@import "../auth/less/logout.less";
+@import "login.less";
+@import "logout.less";

IPython/html/static/base/less/style.less

@@ -1,4 +1,5 @@
-@import "../base/less/variables.less";
-@import "../base/less/mixins.less";
-@import "../base/less/flexbox.less";
+@import "variables.less";
+@import "mixins.less";
+@import "flexbox.less";
+@import "page.less";
 

IPython/html/static/tree/less/style.less

@@ -1,2 +1,2 @@
-@import "../tree/less/altuploadform.less";
-@import "../tree/less/tree.less";
+@import "altuploadform.less";
+@import "tree.less";