zsh-completion: add 'dump_spec' back again

priv/shell-completion/zsh/_rebar

@@ -52,6 +52,7 @@ _rebar () {
         'version[Show version information]' \
         'apps[Application names to process]:' \
         'case[Common Test case]:' \
+        'dump_spec[Dump reltool spec]::flag:(1)' \
         'jobs[Number of workers]::workers:(0 1 2 3 4 5 6 7 8 9)' \
         'suites[Common Test suites]::suite name:_path_files -W "(src test)" -g "*.erl(:r)"' \
         'verbose[Verbosity level]::verbosity level:(0 1 2 3)' \