Add content type header (#121)

* fix: switchbot api is stricter, add missing content-type header

Author: bigboxer23

pom.xml

@@ -4,7 +4,7 @@
 
   <groupId>com.bigboxer23</groupId>
   <artifactId>switchbotapi-java</artifactId>
-  <version>1.2.2</version>
+  <version>1.2.3</version>
 
   <name>switchbotapi-java</name>
   <url>https://github.com/bigboxer23/switchbotapi-java</url>
@@ -98,7 +98,7 @@
             <threadCount>4</threadCount>
             <useUnlimitedThreads>false</useUnlimitedThreads>
             <skipITs>${!integration}</skipITs>
-	          <rerunFailingTestsCount>1</rerunFailingTestsCount>
+            <rerunFailingTestsCount>1</rerunFailingTestsCount>
           </configuration>
           <executions>
             <execution>

src/main/java/com/bigboxer23/switch_bot/SwitchBotApi.java

@@ -65,7 +65,8 @@ protected RequestBuilderCallback addAuth() {
 				builder.addHeader("Authorization", token)
 						.addHeader("sign", signature)
 						.addHeader("nonce", nonce)
-						.addHeader("t", time);
+						.addHeader("t", time)
+						.addHeader("Content-Type", "application/json; charset=utf-8");
 			} catch (NoSuchAlgorithmException | InvalidKeyException e) {
 				log.warn("exception with auth: ", e);
 			}