Cleanup code in lib/mini_racer.rb and remove tabs

Author: eregon

lib/mini_racer.rb

@@ -75,14 +75,12 @@ def write_heap_snapshot(file_or_io)
 
       if String === file_or_io
         f = File.open(file_or_io, "w")
-	implicit = true
+        implicit = true
       else
         f = file_or_io
       end
 
-      if !(File === f)
-        raise ArgumentError, "file_or_io"
-      end
+      raise ArgumentError, "file_or_io" unless File === f
 
       f.write(heap_snapshot())
     ensure

test/mini_racer_test.rb

@@ -11,8 +11,8 @@ class MiniRacerTest < Minitest::Test
   # --stress_snapshot works around a bogus debug assert in V8
   # that terminates the process with the following error:
   #
-  #	Fatal error in ../deps/v8/src/heap/read-only-spaces.cc, line 70
-  #	Check failed: read_only_blob_checksum_ == snapshot_checksum (<unprintable> vs. 1099685679).
+  # Fatal error in ../deps/v8/src/heap/read-only-spaces.cc, line 70
+  # Check failed: read_only_blob_checksum_ == snapshot_checksum (<unprintable> vs. 1099685679).
   MiniRacer::Platform.set_flags! :stress_snapshot
 
   def test_locale_mx