doxygen: normalize output directory to 'docs'

Other MediaWiki extensions use 'docs' as the Doxygen output directory.

Bug: T27978
Change-Id: I14081f4fd74b6b76d58144563f95fc0f8f9aae95

.gitignore

@@ -1,9 +1,8 @@
-node_modules
-docs
-composer.lock
-vendor
-doc
-.eslintcache
+/node_modules
+/docs
+/composer.lock
+/vendor
+/.eslintcache
 
 # Editors
 *.kate-swp

Doxyfile

@@ -3,7 +3,7 @@
 PROJECT_NAME           = Thanks
 PROJECT_BRIEF          = "MediaWiki Thanks extension"
 
-OUTPUT_DIRECTORY       = doc
+OUTPUT_DIRECTORY       = docs
 
 JAVADOC_AUTOBRIEF      = YES
 QT_AUTOBRIEF           = YES