Update Twitter Bootstrap upto v3.1.1.

_assets/vendor/bootstrap/less/button-groups.less

@@ -37,18 +37,17 @@
 
 // Optional: Group multiple button groups together for a toolbar
 .btn-toolbar {
-  .clearfix();
+  margin-left: -5px; // Offset the first child's margin
+  &:extend(.clearfix all);
 
-  .btn-group {
+  .btn-group,
+  .input-group {
     float: left;
   }
-  // Space out series of button groups
   > .btn,
-  > .btn-group {
-    + .btn,
-    + .btn-group {
-      margin-left: 5px;
-    }
+  > .btn-group,
+  > .input-group {
+    margin-left: 5px;
   }
 }
 
@@ -97,9 +96,9 @@
 //
 // Remix the default button sizing classes into new ones for easier manipulation.
 
-.btn-group-xs > .btn { .btn-xs(); }
-.btn-group-sm > .btn { .btn-sm(); }
-.btn-group-lg > .btn { .btn-lg(); }
+.btn-group-xs > .btn { &:extend(.btn-xs); }
+.btn-group-sm > .btn { &:extend(.btn-sm); }
+.btn-group-lg > .btn { &:extend(.btn-lg); }
 
 
 // Split button dropdowns
@@ -157,7 +156,7 @@
 
   // Clear floats so dropdown menus can be properly placed
   > .btn-group {
-    .clearfix();
+    &:extend(.clearfix all);
     > .btn {
       float: none;
     }
@@ -188,13 +187,13 @@
 .btn-group-vertical > .btn-group:not(:first-child):not(:last-child) > .btn {
   border-radius: 0;
 }
-.btn-group-vertical > .btn-group:first-child {
+.btn-group-vertical > .btn-group:first-child:not(:last-child) {
   > .btn:last-child,
   > .dropdown-toggle {
     .border-bottom-radius(0);
   }
 }
-.btn-group-vertical > .btn-group:last-child > .btn:first-child {
+.btn-group-vertical > .btn-group:last-child:not(:first-child) > .btn:first-child {
   .border-top-radius(0);
 }