Fix button spinner (#391)

This somehow got broken with some changes to the button css.

Author: frankieroberto

app/assets/sass/components/_button.scss

@@ -37,7 +37,7 @@
     height: 25px;
     width: 25px;
     background: transparent url('data:image/svg+xml,<svg height="200" viewBox="0 0 200 200" width="200" xmlns="http://www.w3.org/2000/svg">%0A  <g fill="none" fill-rule="evenodd">%0A    <path%0A        d="m100 0v13.0000106c-.0149985-.0000068-.0299979-.0000106-.0449982-.0000106-48.0239214 0-86.9550018 38.9310804-86.9550018 86.9550018 0 48.0239212 38.9310804 86.9550022 86.9550018 86.9550022 48.0089212 0 86.9306812-38.906764 86.9549902-86.910004h13.090008c0 55.228475-44.771525 100-100 100s-100-44.771525-100-100 44.771525-100 100-100z"%0A        fill="%23e5e5e5"/>%0A    <path%0A        d="m0 100h13.0000106zm100 86.909993v13.090007zm100-86.909993h-13.090007c.000007-.0149985.000011-.0299979.000011-.0449982 0-48.0089211-38.906764-86.9306807-86.910004-86.9549904v-13.0000114c55.228475 0 100 44.771525 100 100z"%0A        fill="%23367c42"/>%0A  </g>%0A</svg>') no-repeat;
-    background-size: 25px 25px;
+    background-size: 21px 21px;
     -webkit-animation-name: spin;
     animation-name: spin;
     -webkit-animation-duration: .75s;