doc: Fixing proguide typo [ci skip]

doc/src/asciidoc/ch01/building.asc

@@ -62,7 +62,7 @@ it to your 'pom' as a dependency.
 .The 'clean' task is your friend
 =====
 Out of all the available tasks, there's one that will keep you out
-of trouble: *clean*. While Gradle is very smart when it comes to figure
+of trouble: *clean*. While Gradle is very smart when it comes to figuring
 out which dependencies have been modified and need to be rebuilt, there's
 nothing like the extra confidence that a good old +clean+ gives. When
 in doubt, +gradle clean+.