Apply prefer-const lint rule

lib/extension-wrapper.js

@@ -27,7 +27,7 @@ function errorToFault(err) {
 
   if (!err.name) return { code: "ext", message: `${err}` };
 
-  let fault = {
+  const fault = {
     code: `ext.${err.name}`,
     message: err.message,
     detail: {
@@ -39,7 +39,7 @@ function errorToFault(err) {
   if (err.stack) {
     fault.detail.stack = err.stack;
     // Trim the stack trace
-    let stackTrimIndex = fault.detail.stack.match(
+    const stackTrimIndex = fault.detail.stack.match(
       /\s+at\s[^\s]+\s\(.*extension-wrapper\.js:.+\)/
     );
     if (stackTrimIndex)
@@ -50,7 +50,7 @@ function errorToFault(err) {
 }
 
 process.on("uncaughtException", err => {
-  let fault = errorToFault(err);
+  const fault = errorToFault(err);
   jobs.forEach(jobId => {
     process.send([jobId, fault]);
   });
@@ -62,7 +62,7 @@ process.on("message", message => {
   jobs.add(message[0]);
 
   if (!script) {
-    let cwd = process.env["GENIEACS_CONFIG_DIR"] + "/ext";
+    const cwd = process.env["GENIEACS_CONFIG_DIR"] + "/ext";
     process.chdir(cwd);
     script = require(`${cwd}/${fileName}`);
   }
@@ -70,7 +70,7 @@ process.on("message", message => {
   const funcName = message[1][0];
 
   if (!script[funcName]) {
-    let fault = {
+    const fault = {
       code: "ext",
       message: `No such function '${funcName}' in extension '${fileName}'`
     };