Merge pull request #259 from marshally/fix_rbenv_gemset_bug

fix bug where "no active gemsets" displayed to STDERR
diff --git a/themes/base.theme.bash b/themes/base.theme.bash
index 9c5bedb..a956ef9 100644
--- a/themes/base.theme.bash
+++ b/themes/base.theme.bash
@@ -132,7 +132,7 @@
 function rbenv_version_prompt {
   if which rbenv &> /dev/null; then
     rbenv=$(rbenv version-name) || return
-    $(rbenv commands | grep -q gemset) && gemset=$(rbenv gemset active) && rbenv="$rbenv@${gemset%% *}"
+    $(rbenv commands | grep -q gemset) && gemset=$(rbenv gemset active 2> /dev/null) && rbenv="$rbenv@${gemset%% *}"
     echo -e "$RBENV_THEME_PROMPT_PREFIX$rbenv$RBENV_THEME_PROMPT_SUFFIX"
   fi
 }