fix: add missing space in text (#245)

Co-authored-by: Benjamin E. Coe <[email protected]>

Author: Trott

Diff for: lib/parse-args.js

@@ -92,7 +92,7 @@ function buildYargs (withCommands = false) {
     .options('allowExternal', {
       default: false,
       type: 'boolean',
-      describe: 'supplying --allowExternal will cause c8 to allow files from outside of your cwd. This applies both to' +
+      describe: 'supplying --allowExternal will cause c8 to allow files from outside of your cwd. This applies both to ' +
         'files discovered in coverage temp files and also src files discovered if using the --all flag.'
     })
     .options('src', {