add fix proposed in pure-css/pure#41 (comment)

public/css/main.css

@@ -1,5 +1,5 @@
 body {
-    font-family: sans-serif;
+    font-family: "proxima-nova", sans-serif;
     color: #777;
 }
 
@@ -77,6 +77,22 @@ dd {
     text-align: center;
 }
 
+/* Putting the font-family to Arial makes sure the
+letter and word spacing collapsing works
+https://github.com/yui/pure/issues/41#issuecomment-22147419 */
+
+.pure-g,
+.pure-g-r {
+    font-family: "Helvetica", "Arial", sans-serif;
+}
+
+/* Declaring the font-family on the children ensures
+that the grid doesn't flow to a new line. */
+.pure-g [class *= "pure-u"],
+.pure-g-r [class *= "pure-u"] {
+    font-family: "proxima-nova", sans-serif;
+}
+
 
 /* --------------------------
  * Header Module Styles