Replace key 'Source' by 'source'

osm.org/browse/changeset/7846436
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osm.org/browse/changeset/7846212
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osm.org/browse/changeset/7846182
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osm.org/browse/changeset/7846134
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osm.org/browse/changeset/7846097
- 34 nodes changed
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osm.org/browse/changeset/7846050
- 54 nodes changed
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osm.org/browse/changeset/7845751
- 97 nodes changed
- 92 ways changed