minor edits to metadata context fields (#763)

minor edits to metadata in two studies:

- Gallagher_2018
- Santini_2013

data/Gallagher_2018/metadata.yml

@@ -83,15 +83,23 @@ locations:
     longitude (deg): 151.28337
     elevation (m): 119.0
     description: dry sclerophyll vegetation on sandstone substrate
-contexts: .na
+contexts:
+- context_property: leaf sample type
+  category: method
+  var_in: replicates of
+  values:
+  - value: leaves
+    description: Measurements on leaves.
+  - value: leaflets
+    description: Measurements on leaflets.
 traits:
 - var_in: leaf_area
   unit_in: mm2
   trait_name: leaf_area
   entity_type: individual
   value_type: mean
   basis_of_value: measurement
-  replicates: replicates of
+  replicates: replicates
   methods: the average area of a single leaf, determined from measurements of 3-81
     leaves per individual
 - var_in: leaf_dry_mass
@@ -100,7 +108,7 @@ traits:
   entity_type: individual
   value_type: mean
   basis_of_value: measurement
-  replicates: replicates of
+  replicates: replicates
   methods: the average dry mass of a single leaf, determined from measurements of
     3-81 leaves per individual
 - var_in: specific_leaf_area
@@ -109,7 +117,7 @@ traits:
   entity_type: individual
   value_type: mean
   basis_of_value: measurement
-  replicates: replicates of
+  replicates: replicates
   methods: the specific leaf area per individual, determined from measurements of
     3-81 leaves per individual
 - var_in: leaf nitrogen content

data/Santini_2013/metadata.yml

@@ -115,7 +115,7 @@ traits:
   entity_type: individual
   value_type: mean
   basis_of_value: measurement
-  replicates: 100--200
+  replicates: 100-200
   methods: To assess the anatomical characteristics of the xylem, we made transverse
     sections of 25 um thickness with a Reichert-Jung sliding microtome (Reichert-Jung,
     Heidelburg, Germany). We photographed the sections using a BX61 microscope (Olympus,