Revert "Safe to append with #<< here after all."

Fixes #1387 ('pry -e' messes with the terminal)

This reverts commit 6ffc748683.

Cc: @havenwood :D

CHANGELOG.md

@@ -13,6 +13,7 @@
 * Fixed bug when `hist --clear` led to ArgumentError ([#1340](https://github.com/pry/pry/pull/1340))
 * Fixed the "uninitialized constant Pry::ObjectPath::StringScanner" exception during autocomplete ([#1330](https://github.com/pry/pry/issues/1330))
 * Secured usage of colours with special characters (RL_PROMPT_START_IGNORE and RL_PROMPT_END_IGNORE) in Pry::Helpers::Text ([#493](https://github.com/pry/pry/issues/493#issuecomment-39232771))
+* Fixed regression with `pry -e` when it messes the terminal ([#1387](https://github.com/pry/pry/issues/1387))
 
 ### 0.10.1
 

lib/pry/cli.rb

@@ -116,7 +116,7 @@ Copyright (c) 2013 John Mair (banisterfiend)
 --
 }
   on :e, :exec=, "A line of code to execute in context before the session starts" do |input|
-    exec_string << input << "\n"
+    exec_string + input + "\n"
   end
 
   on "no-pager", "Disable pager for long output" do