Fix typo (#3422)

assertj-core/src/main/java/org/assertj/core/api/AbstractStringAssert.java

@@ -369,7 +369,7 @@ public SELF usingDefaultComparator() {
    * Verifies that the actual value is equal to expected build using {@link String#format(String stringTemplate, Object... args)}.
    * <p>
    * Note that for this assertion to be called, <b>you must use a format template with parameters</b> otherwise {@link #isEqualTo(Object)} is called which
-   * does not perform any formatting. For example, it you only use {@code %n} in the template they won't be replaced.
+   * does not perform any formatting. For example, if you only use {@code %n} in the template they won't be replaced.
    * <p>
    * Examples:
    * <pre><code class='java'> // assertion succeeds