Update MQTT vendor. Update changelog + bump version.

Author: brocaar

docs/config.toml

@@ -32,4 +32,4 @@ googleAnalytics = "UA-3512995-9"
     weight = 4
 
 [params]
-    version = "2.1.4"
+    version = "2.1.5"

docs/content/install/config.md

@@ -29,11 +29,12 @@ GLOBAL OPTIONS:
    --mqtt-server value    mqtt server (e.g. scheme://host:port where scheme is tcp, ssl or ws) (default: "tcp://127.0.0.1:1883") [$MQTT_SERVER]
    --mqtt-username value  mqtt server username (optional) [$MQTT_USERNAME]
    --mqtt-password value  mqtt server password (optional) [$MQTT_PASSWORD]
+   --mqtt-ca-cert value   mqtt CA certificate file (optional) [$MQTT_CA_CERT]
    --skip-crc-check       skip the CRC status-check of received packets [$SKIP_CRC_CHECK]
    --log-level value      debug=5, info=4, warning=3, error=2, fatal=1, panic=0 (default: 4) [$LOG_LEVEL]
    --help, -h             show help
    --version, -v          print the version
 ```
 
 Both cli arguments and environment-variables can be used to pass configuration
-options.
+options.

docs/content/overview/changelog.md

@@ -8,6 +8,21 @@ menu:
 
 ## Changelog
 
+### 2.1.5
+
+**Improvements:**
+
+* `--gw-mqtt-ca-cert` / `GW_MQTT_CA_CERT` configuration flag was added to
+  specify an optional CA certificate
+  (thanks [@minggi](https://github.com/minggi)).
+
+**Bugfixes:**
+
+* MQTT client library update which fixes an issue where during a failed
+  re-connect the protocol version would be downgraded
+  ([paho.mqtt.golang#116](https://github.com/eclipse/paho.mqtt.golang/issues/116)).
+
+
 ### 2.1.4
 
 * Retry connecting to MQTT broker on startup (thanks @jcampanell-cablelabs).
@@ -70,4 +85,4 @@ menu:
 
 ### 1.0.0
 
-Initial release.
+Initial release.