Recipes: make cwd default to slave_build

scripts/slave/recipes/infra/sphinx_doc_updater.expected/basic.json

Index: scripts/slave/recipes/infra/sphinx_doc_updater.expected/basic.json
diff --git a/scripts/slave/recipes/infra/sphinx_doc_updater.expected/basic.json b/scripts/slave/recipes/infra/sphinx_doc_updater.expected/basic.json
index 678bec5bb2dc2d6e27e639e5b19d15cdaef88d96..8d5eb1d93334e2f2bd304a0ba3a004b1115950d2 100644
--- a/scripts/slave/recipes/infra/sphinx_doc_updater.expected/basic.json
+++ b/scripts/slave/recipes/infra/sphinx_doc_updater.expected/basic.json
@@ -22,6 +22,7 @@
       "infra@HEAD",
       "--force"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
@@ -48,6 +49,7 @@
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "gclient runhooks"
   },
   {
@@ -57,6 +59,7 @@
       "[SLAVE_BUILD]/infra/docgen.py",
       "clean"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "Clean documentation"
   },
   {
@@ -65,6 +68,7 @@
       "-u",
       "[SLAVE_BUILD]/infra/docgen.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "Generate documentation"
   },
   {
@@ -80,6 +84,7 @@
       "[SLAVE_BUILD]/infra/doc/html",
       "gs://chromium-infra-docs/infra"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "gsutil upload",
     "~followup_annotations": [
       "@@@STEP_LINK@Deploy documentation to GCS@https://storage.cloud.google.com/chromium-infra-docs/infra@@@"