Bump the injected piggieback to 0.3.8

It's the first version that supports nREPL 0.4+.

Author: bbatsov

cider.el

@@ -373,7 +373,7 @@ Throws an error if PROJECT-TYPE is unknown."
   "List of dependencies where elements are lists of artifact name and version.
 Added to `cider-jack-in-dependencies' when doing `cider-jack-in-cljs'.")
 (put 'cider-jack-in-cljs-dependencies 'risky-local-variable t)
-(cider-add-to-alist 'cider-jack-in-cljs-dependencies "cider/piggieback" "0.3.6")
+(cider-add-to-alist 'cider-jack-in-cljs-dependencies "cider/piggieback" "0.3.8")
 
 (defvar cider-jack-in-dependencies-exclusions nil
   "List of exclusions for jack in dependencies.

doc/clojurescript.md

@@ -29,7 +29,7 @@ project):
 
 ```clojure
 ;; use whatever are the most recent versions here
-[cider/piggieback "0.3.6"]
+[cider/piggieback "0.3.8"]
 [org.clojure/clojure "1.9.0"]
 ```
 
@@ -148,7 +148,7 @@ documentation lookup, the namespace browser, and macroexpansion).
 [adzerk/boot-cljs-repl   "X.Y.Z"  :scope "test"]
 [pandeiro/boot-http      "X.Y.Z"  :scope "test"]
 [weasel                  "0.7.0"  :scope "test"]
-[cider/piggieback "0.3.6"  :scope "test"] ; not needed for cider-jack-in-cljs
+[cider/piggieback "0.3.8"  :scope "test"] ; not needed for cider-jack-in-cljs
 ```
 
 and this at the end of `build.boot`:
@@ -190,7 +190,7 @@ You can also use [Figwheel](https://github.com/bhauman/lein-figwheel) with CIDER
 2. Add these to your dev `:dependencies`:
 
     ```clojure
-    [cider/piggieback "0.3.6"] ; not needed for cider-jack-in-cljs
+    [cider/piggieback "0.3.8"] ; not needed for cider-jack-in-cljs
     [figwheel-sidecar "0.5.16"] ; use here whatever the current version of figwheel is
     ```
 
@@ -224,7 +224,7 @@ You can also use [Figwheel-main](https://github.com/bhauman/figwheel-main) with
 1. Add this to your dev `:dependencies`:
 
     ```clojure
-    [cider/piggieback "0.3.6"] ; not needed for cider-jack-in-cljs
+    [cider/piggieback "0.3.8"] ; not needed for cider-jack-in-cljs
     ```
 
 2. Add this to your dev `:repl-options` (not needed for `cider-jack-in-cljs`):