use slice_head instead of head for potential tibbles

Change-Id: I1ce68ed52209ebaf22e0e29df9ac7281d83e4bc8
diff --git a/demo/light-verb-construction-ca.R b/demo/light-verb-construction-ca.R
index 51d73c1..fa8093f 100644
--- a/demo/light-verb-construction-ca.R
+++ b/demo/light-verb-construction-ca.R
@@ -20,7 +20,7 @@
   ) %>%
   mutate(LVC = sprintf("[in %s %s](%s)", collocate, lvLemma, webUIRequestUrl)) %>%
   select(LVC, logDice, pmi, ll) %>%
-  head(10) %>%
+  slice_head(10) %>%
   kable(format = "pipe", digits = 2)  %>%
   cat(file = mdFile, sep = "\n", append = TRUE)
 
diff --git a/demo/recursiveCA.R b/demo/recursiveCA.R
index 0f2d104..1536b7a 100644
--- a/demo/recursiveCA.R
+++ b/demo/recursiveCA.R
@@ -20,7 +20,7 @@
   mutate(LVC = sprintf("[%s](%s)", example, webUIRequestUrl)) %>%
   { . ->> ca } %>%
   select(LVC, logDice, pmi, ll) %>%
-  head(50) %>%
+  slice_head(50) %>%
   kable(format = "pipe", digits = 2)  %>%
   cat(file = mdFile, sep = "\n")