Update (most) themes to use new ${ruby_version_prompt} variable.
diff --git a/themes/hawaii50/hawaii50.theme.bash b/themes/hawaii50/hawaii50.theme.bash
index 93cef46..0b1fe3b 100644
--- a/themes/hawaii50/hawaii50.theme.bash
+++ b/themes/hawaii50/hawaii50.theme.bash
@@ -98,7 +98,7 @@
 # Displays virtual info prompt (virtualenv/rvm)
 function virtual_prompt_info() {
     local virtual_env_info=$(virtualenv_prompt)
-    local rvm_info=$(rvm_version_prompt)
+    local rvm_info=$(ruby_version_prompt)
     local virtual_prompt=""
 
     local prefix=${VIRTUAL_THEME_PROMPT_PREFIX}