Adding .less file extension to imports to increase compatibility

Closes #2512

less/font-awesome.less

@@ -3,15 +3,15 @@
  *  License - http://fontawesome.io/license (Font: SIL OFL 1.1, CSS: MIT License)
  */
 
-@import "variables";
-@import "mixins";
-@import "path";
-@import "core";
-@import "larger";
-@import "fixed-width";
-@import "list";
-@import "bordered-pulled";
-@import "spinning";
-@import "rotated-flipped";
-@import "stacked";
-@import "icons";
+@import "variables.less";
+@import "mixins.less";
+@import "path.less";
+@import "core.less";
+@import "larger.less";
+@import "fixed-width.less";
+@import "list.less";
+@import "bordered-pulled.less";
+@import "spinning.less";
+@import "rotated-flipped.less";
+@import "stacked.less";
+@import "icons.less";

src/assets/font-awesome/less/font-awesome.less

@@ -2,15 +2,15 @@
 ---
 {% include license-code.less %}
 
-@import "variables";
-@import "mixins";
-@import "path";
-@import "core";
-@import "larger";
-@import "fixed-width";
-@import "list";
-@import "bordered-pulled";
-@import "spinning";
-@import "rotated-flipped";
-@import "stacked";
-@import "icons";
+@import "variables.less";
+@import "mixins.less";
+@import "path.less";
+@import "core.less";
+@import "larger.less";
+@import "fixed-width.less";
+@import "list.less";
+@import "bordered-pulled.less";
+@import "spinning.less";
+@import "rotated-flipped.less";
+@import "stacked.less";
+@import "icons.less";