Fix travis build

powerlevel9k.zsh-theme

@@ -1307,7 +1307,8 @@ prompt_root_indicator() {
 ################################################################
 # Segment to display Rust version number
 prompt_rust_version() {
-  local rust_version=$(command rustc --version 2>/dev/null)
+  local rust_version
+  rust_version=$(command rustc --version 2>/dev/null)
   # Remove "rustc " (including the whitespace) from the beginning
   # of the version string and remove everything after the next
   # whitespace. This way we'll end up with only the version.