typo fix

Author: schmalliso

source/reference/ulimit.txt

@@ -200,7 +200,7 @@ example:
 Each ``limit`` stanza sets the "soft" limit to the first value specified and the "hard"
 limit to the second.
 
-After after changing ``limit`` stanzas, ensure that the changes take
+After changing ``limit`` stanzas, ensure that the changes take
 effect by restarting the application services, using the following
 form:
 
@@ -239,7 +239,7 @@ example:
 Each ``systemd`` limit directive sets both the "hard" and "soft" limits to the value
 specified.
 
-After after changing ``limit`` stanzas, ensure that the changes take
+After changing ``limit`` stanzas, ensure that the changes take
 effect by restarting the application services, using the following
 form: