Fix build script (#351)

.gitignore

@@ -5,4 +5,5 @@ laconic-so
 laconic_stack_orchestrator.egg-info
 __pycache__
 *~
-build
+package
+app/data/build_tag.txt

scripts/build_shiv_package.sh

@@ -1,4 +1,4 @@
 # Builds the shiv "package" for distribution
 mkdir -p ./package
-version_string=$( ./app/data/version.txt )
+version_string=$( ./scripts/create_build_tag_file.sh )
 shiv -c laconic-so -o package/laconic-so-${version_string} .