add trailing newline when libraries and platform installation fail

Author: Alberto Iannaccone

arduino-ide-extension/src/node/boards-service-impl.ts

@@ -436,7 +436,7 @@ export class BoardsServiceImpl
           chunk: `Failed to install platform: ${item.id}.\n`,
         });
         this.responseService.appendToOutput({
-          chunk: error.toString(),
+          chunk: `${error.toString()}\n`,
         });
         reject(error);
       });

arduino-ide-extension/src/node/library-service-impl.ts

@@ -293,7 +293,7 @@ export class LibraryServiceImpl
           }.\n`,
         });
         this.responseService.appendToOutput({
-          chunk: error.toString(),
+          chunk: `${error.toString()}\n`,
         });
         reject(error);
       });