rename Polkadot to Substrate in the license header via following four commands (#614)

git grep -l 'This file is part of Polkadot' | xargs sed -i 's/This file is part of Polkadot/This file is part of Substrate/g'
    git grep -l 'Polkadot is free software' | xargs sed -i 's/Polkadot is free software/Substrate is free software/g'
    git grep -l 'Polkadot is distributed in the hope' | xargs sed -i 's/Polkadot is distributed in the hope/Substrate is distributed in the hope/g'
    git grep -l 'along with Polkadot' | xargs sed -i 's/along with Polkadot/along with Substrate/g'

substrate/substrate/environmental/src/lib.rs

@@ -1,18 +1,18 @@
 // Copyright 2017 Parity Technologies (UK) Ltd.
-// This file is part of Polkadot.
+// This file is part of Substrate.
 
-// Polkadot is free software: you can redistribute it and/or modify
+// Substrate is free software: you can redistribute it and/or modify
 // it under the terms of the GNU General Public License as published by
 // the Free Software Foundation, either version 3 of the License, or
 // (at your option) any later version.
 
-// Polkadot is distributed in the hope that it will be useful,
+// Substrate is distributed in the hope that it will be useful,
 // but WITHOUT ANY WARRANTY; without even the implied warranty of
 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 // GNU General Public License for more details.
 
 // You should have received a copy of the GNU General Public License
-// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 
 //! Safe global references to stack variables.
 //!

substrate/substrate/environmental/with_std.rs

@@ -1,18 +1,18 @@
 // Copyright 2018 Parity Technologies (UK) Ltd.
-// This file is part of Polkadot.
+// This file is part of Substrate.
 
-// Polkadot is free software: you can redistribute it and/or modify
+// Substrate is free software: you can redistribute it and/or modify
 // it under the terms of the GNU General Public License as published by
 // the Free Software Foundation, either version 3 of the License, or
 // (at your option) any later version.
 
-// Polkadot is distributed in the hope that it will be useful,
+// Substrate is distributed in the hope that it will be useful,
 // but WITHOUT ANY WARRANTY; without even the implied warranty of
 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 // GNU General Public License for more details.
 
 // You should have received a copy of the GNU General Public License
-// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 
 #[doc(hidden)]
 pub mod imp {

substrate/substrate/environmental/without_std.rs

@@ -1,18 +1,18 @@
 // Copyright 2018 Parity Technologies (UK) Ltd.
-// This file is part of Polkadot.
+// This file is part of Substrate.
 
-// Polkadot is free software: you can redistribute it and/or modify
+// Substrate is free software: you can redistribute it and/or modify
 // it under the terms of the GNU General Public License as published by
 // the Free Software Foundation, either version 3 of the License, or
 // (at your option) any later version.
 
-// Polkadot is distributed in the hope that it will be useful,
+// Substrate is distributed in the hope that it will be useful,
 // but WITHOUT ANY WARRANTY; without even the implied warranty of
 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 // GNU General Public License for more details.
 
 // You should have received a copy of the GNU General Public License
-// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 
 #[doc(hidden)]
 pub mod imp {