ecosystem -> ecosystems (#196)

Author: tdhock

ecosystems/index.md

@@ -4,5 +4,5 @@
 
 Our packages can be divided into three non-exclusive ecosystems:
 - [Linear Algebra](/ecosystems/linear-algebra/): Packages for dealing with matrices and matrix-like objects. For instance, for solving linear systems, or linear least-squares problems.
-- [Models](/ecosystem/models/): Packages that define and access optimization models.
-- [Solvers](/ecosystem/solvers/): Packages related to our solvers and the development of other solvers.
+- [Models](/ecosystems/models/): Packages that define and access optimization models.
+- [Solvers](/ecosystems/solvers/): Packages related to our solvers and the development of other solvers.