Handle git release tag properly

Build process will check current commit and if it is tagged
starting with a `v` then it will create `prerelease.txt` file in
the top directory.

scripts/build.sh

@@ -1,5 +1,9 @@
 #!/usr/bin/env bash
 
+if [[ "$(git tag --points-at HEAD 2>/dev/null)"=="v*" ]]; then
+	touch prerelease.txt
+fi
+
 if [ -z "$1" ]; then
     BUILD_TYPE=Release
 else
@@ -20,4 +24,4 @@ fi
 if [ -z $CI ]; then
 	echo "Installing solc and soltest"
 	install solc/solc /usr/local/bin && install test/soltest /usr/local/bin
-fi
+fi