Fix a regression with bolded buttons

Since removing the --gr-button @apply customization buttons are bolded
when they have keyboard focus. That is a regression and is fixed by this
change.

Note that `paper-button` rules trump `:host` rules in paper-button.

Change-Id: I74131118c62d7955d4f0746459cfbe90c3439f20
diff --git a/polygerrit-ui/app/elements/shared/gr-button/gr-button.ts b/polygerrit-ui/app/elements/shared/gr-button/gr-button.ts
index 8dc23e2..ea5b5bb 100644
--- a/polygerrit-ui/app/elements/shared/gr-button/gr-button.ts
+++ b/polygerrit-ui/app/elements/shared/gr-button/gr-button.ts
@@ -88,7 +88,9 @@
           background-color: var(--background-color);
           color: var(--text-color);
           display: flex;
-          font-family: inherit;
+          font-family: var(--font-family, inherit);
+          /** Without this '.keyboard-focus' buttons will get bolded. */
+          font-weight: var(--font-weight-normal, inherit);
           justify-content: center;
           margin: var(--margin, 0);
           min-width: var(--border, 0);