shiny-demo: switch to light theme

Change-Id: I486191e9117839476c470b09267b674fe4ca67cc
diff --git a/demo/shiny-apps/frequency_curves/server.R b/demo/shiny-apps/frequency_curves/server.R
index d1e3da4..655c51f 100644
--- a/demo/shiny-apps/frequency_curves/server.R
+++ b/demo/shiny-apps/frequency_curves/server.R
@@ -33,7 +33,8 @@
                        paste(vc, years),
                        as.alternatives = as.alternatives) %>%
     hc_freq_by_year_ci(as.alternatives, smooth = T) %>%
-    hc_add_theme(hc_theme_ids_dark())
+    hc_yAxis(title = list(text = "Instanzen pro Million Wörter")) %>%
+    hc_add_theme(hc_theme_ids_light()) %>%
     hc_caption(text = paste(
       "Frequenzverläufe (mit 95%-Konfidenzbändern) im",
       "<a href='http://www.dereko.de'>Deutschen Referenzkorpus DeReKo</a>",