Fix typo in geoparquet.md (#86)

Author: kylebarron

format-specs/geoparquet.md

@@ -31,7 +31,7 @@ All file-level metadata should be included under the "geo" key in the parquet me
 | ------------------ | ------ | -------------------------------------------------------------------- |
 | version     		 | string | **REQUIRED** The version of the geoparquet metadata standard used when writing.   |
 | primary_column     | string | **REQUIRED** The name of the "primary" geometry column.                |
-| columns            | Map<key, [Colum Metadata](#column-metadata)> | **REQUIRED** Metadata about geometry columns, with each key is the name of a geometry column in the table. |
+| columns            | Map<key, [Column Metadata](#column-metadata)> | **REQUIRED** Metadata about geometry columns, with each key is the name of a geometry column in the table. |
 
 At this level, additional implementation-specific fields (e.g. library name) are allowed, and thus readers should be robust in ignoring those.