Use os.tmpdir() to find a legitimate temp directory across OSes

Fixes #25

pretty-diff.js

@@ -1,6 +1,8 @@
 #!/usr/bin/env node
 
 var fs = require( "fs" );
+var path = require( "path" );
+var os = require( "os" );
 var open = require( "open" );
 var diff = require( "./diff" );
 
@@ -28,6 +30,7 @@ diff( process.argv.slice( 2 ).join( " " ), function( error, parsedDiff ) {
 function generatePrettyDiff( parsedDiff ) {
 	var template = fs.readFileSync( __dirname + "/template.html", "utf8" );
 	var diffHtml = "";
+	var tempPath = path.join( os.tmpdir(), "diff.html" );
 
 	for ( var file in parsedDiff ) {
 		diffHtml += "<h2>" + file + "</h2>" +
@@ -36,8 +39,8 @@ function generatePrettyDiff( parsedDiff ) {
 		"</div></div>";
 	}
 
-	fs.writeFileSync( "/tmp/diff.html", template.replace( "{{diff}}", diffHtml ) );
-	open( "/tmp/diff.html" );
+	fs.writeFileSync( tempPath, template.replace( "{{diff}}", diffHtml ) );
+	open( tempPath );
 }
 
 var markUpDiff = function() {