Merge #37: fix --detach-sig typo in gitian-building.md

e179f08 fix --detach-sig typo in gitian-building.md (fivepiece)

Pull request description:

  This probably never broke anything because `gpg` understood what the argument meant anyway, but fix for consistency.
  ```
  sed -i 's/--detach-sig /--detach-sign /g' gitian-building.md
  ```

Tree-SHA512: ebdea4e22d227f873a8b4b809c479ce3d7fe254a997645b4cb65385ef3fca3635041817d9fa3e07ea2924108a0e3b98e4aac79be8e2b8dfe6bedb44a91892623

Author: MarcoFalke

gitian-building.md

@@ -96,9 +96,9 @@ You need to copy these uncommited changes to your host machine, where you can si
 
 ```
 export NAME=satoshi
-gpg --output $VERSION-linux/$NAME/bitcoin-linux-0.16-build.assert.sig --detach-sig 0.16.0rc1-linux/$NAME/bitcoin-linux-0.16-build.assert 
-gpg --output $VERSION-osx-unsigned/$NAME/bitcoin-osx-0.16-build.assert.sig --detach-sig 0.16.0rc1-osx-unsigned/$NAME/bitcoin-osx-0.16-build.assert 
-gpg --output $VERSION-win-unsigned/$NAME/bitcoin-win-0.16-build.assert.sig --detach-sig 0.16.0rc1-win-unsigned/$NAME/bitcoin-win-0.16-build.assert 
+gpg --output $VERSION-linux/$NAME/bitcoin-linux-0.16-build.assert.sig --detach-sign 0.16.0rc1-linux/$NAME/bitcoin-linux-0.16-build.assert 
+gpg --output $VERSION-osx-unsigned/$NAME/bitcoin-osx-0.16-build.assert.sig --detach-sign 0.16.0rc1-osx-unsigned/$NAME/bitcoin-osx-0.16-build.assert 
+gpg --output $VERSION-win-unsigned/$NAME/bitcoin-win-0.16-build.assert.sig --detach-sign 0.16.0rc1-win-unsigned/$NAME/bitcoin-win-0.16-build.assert 
 ```
 
 Make a PR (both the `.assert` and `.assert.sig` files) to the