fix installation script

Author: Maciej Winnicki

install.sh

@@ -297,9 +297,9 @@ echo "$PREFIX: found version ${VERSION} for ${OS}/${ARCH}"
 
 NAME=${BINARY}_${VERSION}_${OS}_${ARCH}
 TARBALL=${NAME}.${FORMAT}
-TARBALL_URL=${GITHUB_DOWNLOAD}/v${VERSION}/${TARBALL}
+TARBALL_URL=${GITHUB_DOWNLOAD}/${VERSION}/${TARBALL}
 CHECKSUM=${BINARY}_checksums.txt
-CHECKSUM_URL=${GITHUB_DOWNLOAD}/v${VERSION}/${CHECKSUM}
+CHECKSUM_URL=${GITHUB_DOWNLOAD}/${VERSION}/${CHECKSUM}
 
 # Adjust binary name if windows
 if [ "$OS" = "windows" ]; then