JamiString: improve some strings

Change-Id: I1557d50ae603d7a45ac192b687cdad92bdaa6684

src/constant/JamiStrings.qml

@@ -216,8 +216,8 @@ Item {
     property string chat: qsTr("Chat")
     property string moreOptions: qsTr("More options")
     property string mosaic: qsTr("Mosaic")
-    property string participantMicIsStillMuted: qsTr("Participant is still muted on his local machine")
-    property string mutedLocally: qsTr("You are still muted on your local machine")
+    property string participantMicIsStillMuted: qsTr("Participant is still muted on their device")
+    property string mutedLocally: qsTr("You are still muted on your device")
     property string participantModIsStillMuted: qsTr("You are still muted by moderator")
     property string mutedByModerator: qsTr("You are muted by a moderator")
     property string moderator: qsTr("Moderator")