Fix typos breaking first if conditional, syntax error

scripts/install_build_environment.sh

@@ -52,6 +52,7 @@ else
 	else
 	    rm opam_temp_version_2_0_4.bin
 	    exit
+	fi
     else
 	echo "opam file hash doesn't match what was recorded at time of signature verification!"
 	echo "(If you actually get this message, you should probably file an issue)"