fix(cli): exclusively is also '-e' for destroy

Make the short option for `--exclusively` always `-e` (used to be `-e`
for `synth` and `deploy`, but `-x` for `destroy).

Fixes #2367.

packages/aws-cdk/bin/cdk.ts

@@ -58,7 +58,7 @@ async function parseCommandLineArguments() {
       .option('ci', { type: 'boolean', desc: 'Force CI detection. Use --no-ci to disable CI autodetection.', default: process.env.CI !== undefined })
       .option('tags', { type: 'array', alias: 't', desc: 'tags to add to the stack (KEY=VALUE)', nargs: 1, requiresArg: true })
     .command('destroy [STACKS..]', 'Destroy the stack(s) named STACKS', yargs => yargs
-      .option('exclusively', { type: 'boolean', alias: 'x', desc: 'only deploy requested stacks, don\'t include dependees' })
+      .option('exclusively', { type: 'boolean', alias: 'e', desc: 'only deploy requested stacks, don\'t include dependees' })
       .option('force', { type: 'boolean', alias: 'f', desc: 'Do not ask for confirmation before destroying the stacks' }))
     .command('diff [STACKS..]', 'Compares the specified stack with the deployed stack or a local template file, and returns with status 1 if any difference is found', yargs => yargs
       .option('exclusively', { type: 'boolean', alias: 'e', desc: 'only diff requested stacks, don\'t include dependencies' })