variables.less: Fix typo in comment for @caret-width-base

Closes twbs/bootstrap-sass#1005
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less/variables.less

@@ -111,7 +111,7 @@
 //** Global background color for active items (e.g., navs or dropdowns).
 @component-active-bg:       @brand-primary;
 
-//** Width of the `border` for generating carets that indicator dropdowns.
+//** Width of the `border` for generating carets that indicate dropdowns.
 @caret-width-base:          4px;
 //** Carets increase slightly in size for larger components.
 @caret-width-large:         5px;