fix random.1 man page

Trailing whitespace on a `\fish` command was causing this build failure:

/private/var/folders/T/fish_doc_build_3RT8yS/random.doxygen:44:
   warning: found </pre> tag without matching <pre>

doc_src/random.txt

@@ -30,12 +30,15 @@ statistically accurate.
 \subsection random-example Example
 
 The following code will count down from a random even number between 10 and 20 to 1:
+
 \fish
 for i in (seq (random 10 2 20) -1 1)
     echo $i
 end
 \endfish
+
 And this will open a random picture from any of the subdirectories:
-\fish 
+
+\fish
 open (random choice **jpg)
 \endfish