Update docs

Author: russcam

docs/aggregations/bucket/histogram/histogram-aggregation-usage.asciidoc

@@ -23,7 +23,7 @@ a => a
 .Histogram("commits", h => h
     .Field(p => p.NumberOfCommits)
     .Interval(100)
-    .Missing(0)
+    .MinimumDocumentCount(1)
     .Order(HistogramOrder.KeyDescending)
     .Offset(1.1)
 )
@@ -37,7 +37,7 @@ new HistogramAggregation("commits")
 {
     Field = Field<Project>(p => p.NumberOfCommits),
     Interval = 100,
-    Missing = 0,
+    MinimumDocumentCount = 1,
     Order = HistogramOrder.KeyDescending,
     Offset = 1.1
 }
@@ -51,7 +51,7 @@ new HistogramAggregation("commits")
     "histogram": {
       "field": "numberOfCommits",
       "interval": 100.0,
-      "missing": 0.0,
+      "min_doc_count": 1,
       "order": {
         "_key": "desc"
       },