Fix spinta package issue

After releasing spinta 0.1.7, I found, that it won't install any
dependencies. After quite lengthy debugging I found, that is is caused
by description having a new line.

Failed a bug report for Poetry:
python-poetry/poetry#3610

pyproject.toml

@@ -1,9 +1,7 @@
 [tool.poetry]
 name = "spinta"
 version = "0.1.7"
-description = """\
-A platform for describing, extracting, transforming and serving open data.
-"""
+description = "A platform for describing, extracting, transforming, loading and serving open data."
 authors = ["Mantas Zimnickas <sirexas@gmail.com>"]
 license = "MIT"
 readme = "README.rst"