Don't wrap enroll button text

The "Leave Current/Switch/Select" Session button was sometimes
wrapping its text if it wasn't given enough horizontal space.
Now it should never wrap, instead stealing space from the
dropdown next to it (or being bumped to a line below the dropdown).

LEARNER-3668

lms/static/sass/views/_course-entitlements.scss

@@ -27,12 +27,13 @@
       height: $baseline*1.5;
       flex-grow: 1;
       letter-spacing: 0;
+      white-space: nowrap;
       background: theme-color("inverse");
       border-color: theme-color("primary");
       color: theme-color("primary");
       text-shadow: none;
       font-size: $font-size-base;
-      padding: 0;
+      padding: 0 $baseline/4;
       box-shadow: none;
       border-radius: $border-radius-sm;
       transition: all 0.4s ease-out;