Fix "ImportError: cannot import name 'Markup' from 'jinja2'" (#354)

Update requirements to fix jinja2/markup error

README.md

@@ -41,6 +41,7 @@ Requirements:
 
 Setup:
 - Create a python >=3.6 virtual environment
+- Base requirements are defined in the `requirements.in` file (to ejecute `pip-compile` it's required to update `requirements.txt`)
 - `pip install -r requirements.txt`
 - `npm ci`
 - `lektor server`

requirements.in

@@ -0,0 +1,7 @@
+lektor==3.3.3
+lektor-nl2br==0.2.0
+lektor-twitter-embed==0.2.0
+lektor-youtube-embed==0.2.0
+marshmallow==3.15.0
+python-slugify==4.0.1
+Pillow==8.1.1

requirements.txt

@@ -1,7 +1,84 @@
-lektor>=3
-lektor-nl2br==0.1.1
-lektor-twitter-embed==0.1.0
-lektor-youtube-embed==0.1.1
-marshmallow==3.10.0
+#
+# This file is autogenerated by pip-compile with python 3.8
+# To update, run:
+#
+#    pip-compile
+#
+babel==2.9.1
+    # via lektor
+certifi==2021.10.8
+    # via requests
+charset-normalizer==2.0.12
+    # via requests
+click==8.1.2
+    # via
+    #   flask
+    #   lektor
+exifread==2.3.2
+    # via lektor
+filetype==1.0.10
+    # via lektor
+flask==2.1.1
+    # via lektor
+idna==3.3
+    # via requests
+importlib-metadata==4.11.3
+    # via flask
+inifile==0.4.1
+    # via lektor
+itsdangerous==2.1.2
+    # via flask
+jinja2==3.1.1
+    # via
+    #   flask
+    #   lektor
+lektor==3.3.3
+    # via
+    #   -r requirements.in
+    #   lektor-nl2br
+    #   lektor-twitter-embed
+    #   lektor-youtube-embed
+lektor-nl2br==0.2.0
+    # via -r requirements.in
+lektor-twitter-embed==0.2.0
+    # via -r requirements.in
+lektor-youtube-embed==0.2.0
+    # via -r requirements.in
+markupsafe==2.1.1
+    # via jinja2
+marshmallow==3.15.0
+    # via -r requirements.in
+mistune==0.8.4
+    # via lektor
+packaging==21.3
+    # via marshmallow
+pillow==8.1.1
+    # via -r requirements.in
+pyparsing==3.0.8
+    # via packaging
 python-slugify==4.0.1
-Pillow==8.1.1
+    # via
+    #   -r requirements.in
+    #   lektor
+pytz==2022.1
+    # via babel
+requests[security]==2.27.1
+    # via
+    #   lektor
+    #   lektor-twitter-embed
+text-unidecode==1.3
+    # via python-slugify
+urllib3==1.26.9
+    # via requests
+watchdog==2.1.7
+    # via lektor
+werkzeug==2.1.1
+    # via
+    #   flask
+    #   lektor
+zipp==3.8.0
+    # via importlib-metadata
+
+# The following packages are considered to be unsafe in a requirements file:
+# pip
+# setuptools