fix babel-preset-env version ref (#43)

thiagoarrais · bevacqua · commit 0cf0c36ef302 · 2017-10-02T14:38:45.000-03:00
diff --git a/ch01.asciidoc b/ch01.asciidoc
@@ -147,7 +147,7 @@ To install Babel, enter the following couple of commands into your favorite term
 [source,shell]
 ----
 npm install babel-cli​@6 --save-dev
-npm install babel-preset-env@6 --save-dev
+npm install babel-preset-env@1 --save-dev
 ----
 
 [NOTE]
