FIX bash startup failure (within GOW)

* create the `etc` directory (if needed)

.# DISCUSSION

`bash` requires the `etc` directory for startup. However, `etc` is missing
from the GOW repo. There are current pull requests fixing this issue (see
bmatzelle/gow#192). But, this fixes the the issue while waiting for the GOW
repo to be updated. The fix here is compatible with all of the current possible
future GOW repo fixes.

gow.json

@@ -11,7 +11,11 @@
 	"pre_install": "
 		\"@cscript //NoLogo \"\"$dir\\bin\\gow.vbs\"\" %1\" | Set-Content -force \"$dir\\bin\\gow.bat\"
 	",
-   	"bin": [
+	"post_install": "
+		# create etc directory (required by bash), if needed
+		if (! (test-path \"$dir\\etc\")) { new-item -itemtype directory \"$dir\\etc\" }
+	",
+	"bin": [
 		"bin\\awk.exe",
 		"bin\\basename.exe",
 		"bin\\bash.exe",