Properly override normalize.css' `box-sizing` for all browsers.

Fix #481.

dist/css/ratchet.css

@@ -856,7 +856,9 @@ input[type="color"] {
 }
 
 input[type="search"] {
-  box-sizing: border-box;
+  -webkit-box-sizing: border-box;
+     -moz-box-sizing: border-box;
+          box-sizing: border-box;
   padding: 0 10px;
   font-size: 16px;
   border-radius: 20px;

docs/dist/css/ratchet.css

@@ -856,7 +856,9 @@ input[type="color"] {
 }
 
 input[type="search"] {
-  box-sizing: border-box;
+  -webkit-box-sizing: border-box;
+     -moz-box-sizing: border-box;
+          box-sizing: border-box;
   padding: 0 10px;
   font-size: 16px;
   border-radius: 20px;

sass/forms.scss

@@ -45,7 +45,10 @@ input[type="search"] {
   padding: 0 10px;
   font-size: 16px;
   border-radius: 20px;
-  box-sizing: border-box; // Override content-box in normalize
+  // Override content-box in normalize
+  -webkit-box-sizing: border-box;
+     -moz-box-sizing: border-box;
+          box-sizing: border-box;
 }
 input[type="search"]:focus {
   text-align: left;