Fix #4780: Don't mutate the options object when compiling and transpiling, so that options are correct on subsequent iterations (#4785)

Author: GeoffreyBooth

lib/coffeescript/coffeescript.js

@@ -140,12 +140,14 @@ exports.compile = compile = withPrettyErrors (code, options = {}) ->
     transpiler = options.transpile.transpile
     delete options.transpile.transpile
 
+    transpilerOptions = Object.assign {}, options.transpile
+
     # See https://github.com/babel/babel/issues/827#issuecomment-77573107:
     # Babel can take a v3 source map object as input in `inputSourceMap`
     # and it will return an *updated* v3 source map object in its output.
-    if v3SourceMap and not options.transpile.inputSourceMap?
-      options.transpile.inputSourceMap = v3SourceMap
-    transpilerOutput = transpiler js, options.transpile
+    if v3SourceMap and not transpilerOptions.inputSourceMap?
+      transpilerOptions.inputSourceMap = v3SourceMap
+    transpilerOutput = transpiler js, transpilerOptions
     js = transpilerOutput.code
     if v3SourceMap and transpilerOutput.map
       v3SourceMap = transpilerOutput.map