update log4j-core version (#46)

Author: yotamloe

README.md

@@ -13,7 +13,7 @@ This appender uses  [LogzioSender](https://github.com/logzio/logzio-java-sender)
     <dependency>
         <groupId>io.logz.log4j2</groupId>
         <artifactId>logzio-log4j2-appender</artifactId>
-        <version>1.0.14</version>
+        <version>1.0.15</version>
     </dependency>
 ```
 
@@ -137,6 +137,8 @@ Will send a log to Logz.io that looks like this:
 ```
 
 ### Release notes
+ - 1.0.15
+   - Bump versions of `log4j-core`
  - 1.0.14
    - Bump versions of `log4j-api` and `log4j-core`
  - 1.0.13