refactor: fix linter warnings

Author: mrholek

scss/_icon.scss

@@ -3,7 +3,7 @@
   color: inherit;
   text-align: center;
   vertical-align: -.125rem; // Fix the position of icon
-  fill: currentColor;
+  fill: currentcolor;
   &:not(.icon-c-s):not(.icon-custom-size) {
     @include icon-size($icon-size-base);
 

scss/_placeholders.scss

@@ -3,7 +3,7 @@
   min-height: 1em;
   vertical-align: middle;
   cursor: wait;
-  background-color: currentColor;
+  background-color: currentcolor;
   opacity: $placeholder-opacity-max;
 
   &.btn::before {

scss/_spinners.scss

@@ -29,7 +29,7 @@
   --#{$prefix}spinner-animation-name: spinner-border;
   // scss-docs-end spinner-border-css-vars
 
-  border: var(--#{$prefix}spinner-border-width) solid currentColor;
+  border: var(--#{$prefix}spinner-border-width) solid currentcolor;
   border-right-color: transparent;
 }
 
@@ -66,7 +66,7 @@
   --#{$prefix}spinner-animation-name: spinner-grow;
   // scss-docs-end spinner-grow-css-vars
 
-  background-color: currentColor;
+  background-color: currentcolor;
   opacity: 0;
 }
 

scss/_variables.scss

@@ -787,7 +787,7 @@ $table-border-color:          var(--#{$prefix}border-color) !default;
 $table-striped-order:         odd !default;
 $table-striped-columns-order: even !default;
 
-$table-group-separator-color: currentColor !default;
+$table-group-separator-color: currentcolor !default;
 
 $table-caption-color:         $text-muted !default;
 

scss/helpers/_vr.scss

@@ -4,6 +4,6 @@
   width: 1px;
   min-height: 1em;
   padding: 0;
-  background-color: currentColor;
+  background-color: currentcolor;
   opacity: $hr-opacity;
 }

scss/sidebar/_sidebar-nav.scss

@@ -89,7 +89,7 @@
     font-size: var(--#{$prefix}sidebar-nav-icon-font-size);
     color: var(--#{$prefix}sidebar-nav-link-icon-color);
     text-align: center;
-    fill: currentColor;
+    fill: currentcolor;
     @include transition(inherit);
 
     &:first-child {