Move source to its own directory

This matches how the rest of the build is organized but also hopefully
solves an issue where the VS Code directory is empty because we try to
cache it directly and Travis might be creating it.

.gitignore

@@ -2,3 +2,4 @@ node_modules
 build
 release
 binaries
+source

.travis.yml

@@ -76,4 +76,4 @@ deploy:
 cache:
   yarn: true
   directories:
-    - build/vscode-1.39.2-source
+    - source

scripts/build.ts

@@ -77,11 +77,10 @@ class Builder {
 		const vscodeVersion = this.ensureArgument("vscodeVersion", args[0]);
 		const codeServerVersion = this.ensureArgument("codeServerVersion", args[1]);
 
-		const stagingPath = path.join(this.outPath, "build");
-		const vscodeSourcePath = path.join(stagingPath, `vscode-${vscodeVersion}-source`);
+		const vscodeSourcePath = path.join(this.outPath, "source", `vscode-${vscodeVersion}-source`);
 		const binariesPath = path.join(this.outPath, "binaries");
 		const binaryName = `code-server${codeServerVersion}-vsc${vscodeVersion}-${target}-${arch}`;
-		const finalBuildPath = path.join(stagingPath, `${binaryName}-built`);
+		const finalBuildPath = path.join(this.outPath, "build", `${binaryName}-built`);
 
 		switch (task) {
 			case Task.Binary: