Fixed Javadoc and comment typos

Fixes: #294

api/src/main/java/io/jsonwebtoken/Header.java

@@ -105,6 +105,7 @@ public interface Header<T extends Header<T>> extends Map<String,Object> {
      * an example of a Nested JWT.</p>
      *
      * @param cty the JWT JOSE {@code cty} header value or {@code null} to remove the property from the JSON map.
+     * @return the {@code Header} instance for method chaining.
      */
     T setContentType(String cty);
 
@@ -119,12 +120,13 @@ public interface Header<T extends Header<T>> extends Map<String,Object> {
     /**
      * Sets the JWT <code>zip</code> (Compression Algorithm) header parameter value. A {@code null} value will remove
      * the property from the JSON map.
-     * <p>
+     *
      * <p>The compression algorithm is NOT part of the <a href="https://tools.ietf.org/html/draft-ietf-oauth-json-web-token-25">JWT specification</a>
      * and must be used carefully since, is not expected that other libraries (including previous versions of this one)
      * be able to deserialize a compressed JTW body correctly. </p>
      *
      * @param zip the JWT compression algorithm {@code zip} value or {@code null} to remove the property from the JSON map.
+     * @return the {@code Header} instance for method chaining.
      * @since 0.6.0
      */
     T setCompressionAlgorithm(String zip);

api/src/main/java/io/jsonwebtoken/JwtBuilder.java

@@ -480,7 +480,7 @@ public interface JwtBuilder extends ClaimsMutator<JwtBuilder> {
      * <p>The JWT family of specifications defines compression only for JWE (Json Web Encryption)
      * tokens.  Even so, JJWT will also support compression for JWS tokens as well if you choose to use it.
      * However, be aware that <b>if you use compression when creating a JWS token, other libraries may not be able to
-     * parse that JWS token</b>.  When using compression for JWS tokens, be sure that that all parties accessing the
+     * parse that JWS token</b>.  When using compression for JWS tokens, be sure that all parties accessing the
      * JWS token support compression for JWS.</p>
      *
      * <p>Compression when creating JWE tokens however should be universally accepted for any

impl/src/main/java/io/jsonwebtoken/impl/JwtMap.java

@@ -83,13 +83,13 @@ public class JwtMap implements Map<String, Object> {
         } else if (v instanceof Number) {
             // https://github.com/jwtk/jjwt/issues/122:
             // The JWT RFC *mandates* NumericDate values are represented as seconds.
-            // Because Because java.util.Date requires milliseconds, we need to multiply by 1000:
+            // Because java.util.Date requires milliseconds, we need to multiply by 1000:
             long seconds = ((Number) v).longValue();
             v = seconds * 1000;
         } else if (v instanceof String) {
             // https://github.com/jwtk/jjwt/issues/122
             // The JWT RFC *mandates* NumericDate values are represented as seconds.
-            // Because Because java.util.Date requires milliseconds, we need to multiply by 1000:
+            // Because java.util.Date requires milliseconds, we need to multiply by 1000:
             try {
                 long seconds = Long.parseLong((String) v);
                 v = seconds * 1000;