Update bootstrap

_sass/bootstrap/_functions.scss

@@ -8,7 +8,7 @@
   $prev-key: null;
   $prev-num: null;
   @each $key, $num in $map {
-    @if $prev-num == null or unit($num) == "%" {
+    @if $prev-num == null or unit($num) == "%" or unit($prev-num) == "%" {
       // Do nothing
     } @else if not comparable($prev-num, $num) {
       @warn "Potentially invalid value for #{$map-name}: This map must be in ascending order, but key '#{$key}' has value #{$num} whose unit makes it incomparable to #{$prev-num}, the value of the previous key '#{$prev-key}' !";
@@ -48,6 +48,17 @@
   @return $string;
 }
 
+// See https://codepen.io/kevinweber/pen/dXWoRw
+@function escape-svg($string) {
+  @if str-index($string, "data:image/svg+xml") {
+    @each $char, $encoded in $escaped-characters {
+      $string: str-replace($string, $char, $encoded);
+    }
+  }
+
+  @return $string;
+}
+
 // Color contrast
 @function color-yiq($color, $dark: $yiq-text-dark, $light: $yiq-text-light) {
   $r: red($color);
@@ -84,3 +95,40 @@
 
   @return mix($color-base, $color, $level * $theme-color-interval);
 }
+
+// Return valid calc
+@function add($value1, $value2, $return-calc: true) {
+  @if $value1 == null {
+    @return $value2;
+  }
+
+  @if $value2 == null {
+    @return $value1;
+  }
+
+  @if type-of($value1) == number and type-of($value2) == number and comparable($value1, $value2) {
+    @return $value1 + $value2;
+  }
+
+  @return if($return-calc == true, calc(#{$value1} + #{$value2}), $value1 + unquote(" + ") + $value2);
+}
+
+@function subtract($value1, $value2, $return-calc: true) {
+  @if $value1 == null and $value2 == null {
+    @return null;
+  }
+
+  @if $value1 == null {
+    @return -$value2;
+  }
+
+  @if $value2 == null {
+    @return $value1;
+  }
+
+  @if type-of($value1) == number and type-of($value2) == number and comparable($value1, $value2) {
+    @return $value1 - $value2;
+  }
+
+  @return if($return-calc == true, calc(#{$value1} - #{$value2}), $value1 + unquote(" - ") + $value2);
+}