Update gitignore (sorry)

electron/node_modules/electron-osx-sign/bin/electron-osx-flat-usage.txt

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+
+NAME
+  electron-osx-flat -- product building for Electron apps
+
+SYNOPSIS
+  electron-osx-flat app [options ...]
+
+DESCRIPTION
+  app
+    Path to the application package.
+    Needs file extension ``.app''.
+
+  --help
+    Flag to display all commands.
+
+  --identity=identity
+    Name of certificate to use when signing.
+    Default to selected with respect to --platform from --keychain specified or keychain by system default.
+
+  --identity-validation, --no-identity-validation
+    Flag to enable/disable validation for the signing identity.
+
+  --install=install-path
+    Path to install the bundle.
+    Default to ``/Applications''.
+
+  --keychain=keychain
+    The keychain name.
+    Default to system default keychain.
+
+  --platform=platform
+    Build platform of Electron.
+    Allowed values: ``darwin'', ``mas''.
+    Default to auto detect from application bundle.
+
+  --pkg
+    Path to the output the flattened package.
+    Needs file extension ``.pkg''.
+
+  --scripts
+    Path to a directory containing pre and/or post install scripts.