improve compliance with LESS's strictMath

less/type.less

@@ -61,7 +61,7 @@ p {
 
 .lead {
   margin-bottom: @line-height-computed;
-  font-size: floor(@font-size-base * 1.15);
+  font-size: floor((@font-size-base * 1.15));
   font-weight: 200;
   line-height: 1.4;
 

less/variables.less

@@ -45,18 +45,18 @@
 @font-family-base:        @font-family-sans-serif;
 
 @font-size-base:          14px;
-@font-size-large:         ceil(@font-size-base * 1.25); // ~18px
-@font-size-small:         ceil(@font-size-base * 0.85); // ~12px
+@font-size-large:         ceil((@font-size-base * 1.25)); // ~18px
+@font-size-small:         ceil((@font-size-base * 0.85)); // ~12px
 
-@font-size-h1:            floor(@font-size-base * 2.6); // ~36px
-@font-size-h2:            floor(@font-size-base * 2.15); // ~30px
-@font-size-h3:            ceil(@font-size-base * 1.7); // ~24px
-@font-size-h4:            ceil(@font-size-base * 1.25); // ~18px
+@font-size-h1:            floor((@font-size-base * 2.6)); // ~36px
+@font-size-h2:            floor((@font-size-base * 2.15)); // ~30px
+@font-size-h3:            ceil((@font-size-base * 1.7)); // ~24px
+@font-size-h4:            ceil((@font-size-base * 1.25)); // ~18px
 @font-size-h5:            @font-size-base;
-@font-size-h6:            ceil(@font-size-base * 0.85); // ~12px
+@font-size-h6:            ceil((@font-size-base * 0.85)); // ~12px
 
 @line-height-base:        1.428571429; // 20/14
-@line-height-computed:    floor(@font-size-base * @line-height-base); // ~20px
+@line-height-computed:    floor((@font-size-base * @line-height-base)); // ~20px
 
 @headings-font-family:    inherit;
 @headings-font-weight:    500;
@@ -263,7 +263,7 @@
 @navbar-height:                    50px;
 @navbar-margin-bottom:             @line-height-computed;
 @navbar-border-radius:             @border-radius-base;
-@navbar-padding-horizontal:        floor(@grid-gutter-width / 2);
+@navbar-padding-horizontal:        floor((@grid-gutter-width / 2));
 @navbar-padding-vertical:          ((@navbar-height - @line-height-computed) / 2);
 
 @navbar-default-color:             #777;
@@ -374,7 +374,7 @@
 @jumbotron-color:                inherit;
 @jumbotron-bg:                   @gray-lighter;
 @jumbotron-heading-color:        inherit;
-@jumbotron-font-size:            ceil(@font-size-base * 1.5);
+@jumbotron-font-size:            ceil((@font-size-base * 1.5));
 
 
 // Form states and alerts