Fixed a few comment typos which were driving us nuts

library/scss/_768up.scss

@@ -28,7 +28,7 @@ LAYOUT & GRID STYLES
 }
 
 /*********************
-HEADER SYTLES
+HEADER STYLES
 *********************/
 
 .header {}

library/scss/_base.scss

@@ -147,7 +147,7 @@ h5, .h5 {
 }
 
 /*********************
-HEADER SYTLES
+HEADER STYLES
 *********************/
 
 .header {}

library/scss/_mixins.scss

@@ -147,7 +147,7 @@ span.amp {
 }
 
 /*********************
-TRANISTION
+TRANSITION
 *********************/
 
 /*