Fix documentation typo

Co-authored-by: intrigus-lgtm <60750685+intrigus-lgtm@users.noreply.github.com>

Author: joefarebrother

java/ql/src/semmle/code/java/dataflow/internal/TaintTrackingUtil.qll

@@ -772,7 +772,7 @@ private predicate formatStep(Expr tracked, Expr sink) {
 /**
  * A local variable that is assigned a `Formatter`.
  * Writing tainted data to such a formatter causes the underlying
- * `OutputStream` or `Appenable` to be tainted.
+ * `OutputStream` or `Appendable` to be tainted.
  */
 private class FormatterVar extends LocalVariableDecl {
   FormatterVar() {